Think! Don't substitute!

Algebra Level 2

1 + a + 2 b + 3 c + 2 a b + 3 a c + 6 b c + 6 a b c 1 + a + 2b + 3c + 2ab + 3ac + 6bc + 6abc

We are given that a = 999 , b = 666 , c = 333 a = \color{#D61F06}{999} , b = \color{#3D99F6}{666} , c = \color{#20A900}{333} . Find the value of the expression above.

Hint: Try to factorize the expression.


The answer is 1333000000.

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24 solutions

Nihar Mahajan
Feb 11, 2015

1 + a + 2 b + 3 c + 2 a b + 3 a c + 6 b c + 6 a b c 1 + a + 2b + 3c + 2ab + 3ac + 6bc + 6abc

= 6 a b c + 2 a b + 3 a c + a + 6 b c + 2 b + 3 c + 1 = 6abc + 2ab + 3ac + a + 6bc + 2b + 3c + 1

= 2 a b ( 3 c + 1 ) + a ( 3 c + 1 ) + 2 b ( 3 c + 1 ) + 1 ( 3 c + 1 ) = 2ab(3c + 1) + a(3c + 1) + 2b(3c + 1) + 1(3c + 1)

= ( 2 a b + a + 2 b + 1 ) ( 3 c + 1 ) = (2ab + a + 2b + 1)(3c + 1)

= [ a ( 2 b + 1 ) + 1 ( 2 b + 1 ) ] ( 3 c + 1 ) = [a(2b + 1) + 1(2b + 1)](3c + 1)

= ( a + 1 ) ( 2 b + 1 ) ( 3 c + 1 ) = (a + 1)(2b + 1)(3c + 1)

= ( 999 + 1 ) ( 2 ( 666 ) + 1 ) ( 3 ( 333 ) + 1 ) = (999 + 1)(2(666) + 1)(3(333) + 1)

= ( 1000 ) ( 1333 ) ( 1000 ) = (1000)(1333)(1000)

= 1333000000 =\huge \boxed{1333000000}

Extraordinary

Kodandarao Kolati - 5 years, 5 months ago

Nicely done! What I did was I started grouping together like terms; starting with all the a's:

1 + a + 2b + 3c + 2ab + 3ac + 6bc + 6abc

By rearranging the terms, the expression becomes more easily factored:

2ac + 2ab + a + 6abc + 6bc + 2b + 3c +1

Factor out one 'a' from the first group of paired terms:

a (2b + 6bc + 3c + 1) + (6bc + 2b + 3c + 1)

It then took a few minutes for my eyes to interpret the above simply as:

6bc + 2b + 3c + 1 ( a + 1) ==》 the first sequence of terms factors out!

Breaking down even cleaner for the first sequence, it can factor out further:

3c (2b + 1) + (2b + 1) but do not forget the (a + 1) multiplied with that!

We know a = 999 b = 666 and c = 333; plugging in those numbers is strategic in the next few steps:

Just like before, the (2b + 1) from the previous expression can factor out:

(2b + 1) ( 3c + 1) * (a + 1) ==》 this gives a friendlier layout to work more efficiently with the numbers provided.

Intuitively, starting out with ( a + 1) would be a good place to start, because a = 999: (999 + 1) = 1000! Easy peezy!

(2b + 1) ( 3c + 1) * (1000)

With a little more work with numbers, finding out the next step can be done by understanding that the expression (3c + 1) is relative to (a + 1) in that 3 × 333 = 999: c = 333 but remember to add on the 1 in the expression 3c + 1!

(2b + 1)(3 × 333 + 1) × 1000 ==》 this is what our expression should look like.

Reduce: (2 [ 666 ] + 1)(1000)(1000) ==》 by placing the 666 in for b in the first term.

Basic math gives us the final answer!

2 × 666 = 1332 + 1 = 1333 (1000) (1000) = 1333000000

Eric Beck - 5 years, 2 months ago

I made all terms c. 36c^3+33c^2+10c+1. Then solved cubic equation

Allen Morrison - 4 years, 5 months ago

For anyone wondering how to spot these patterns unfortunately there is no simple answer. Of course you have to practice on a lot of different and increasingly hard problems until the intuition comes more and more easily to you. As a general rule of thumb is useful to rearrange the problem in such a way to exploit symmetries. Good luck to everyone on the journey to mastery.

Michele Franzoni - 2 years, 1 month ago
  • Replacing a = 3c and b = 2c , we find that: 1 + a + 2 b + 3 c + 2 a b + 3 a c + 6 b c + 6 a b c = 36 c 3 + 33 c 2 + 10 c + 1 1 + a + 2b + 3c + 2ab + 3ac + 6bc + 6abc = 36c^{3} + 33c^{2} + 10c + 1 .
  • Factoring this expression, we have: 36 c 3 + 33 c 2 + 10 c + 1 = ( 3 c + 1 ) 2 ( 4 c + 1 ) 36c^{3} + 33c^{2} + 10c + 1 = (3c + 1)^{2}(4c + 1) .
  • Now, replacing c = 333 , we have:
    ( 3 × 333 + 1 ) 2 ( 4 × 333 + 1 ) = (3\times333 + 1)^{2}(4\times333 + 1) = ( 1000 ) 2 ( 1333 ) = (1000)^{2}(1333) = 13330000 13330000 .

Did the same, bit didnt know how to solve 3 degree equation

Franklin Junior - 5 years ago

awsum.. gt stuckt in the last step.. goood work dude..

Nithin Nithu - 6 years, 2 months ago

That is exactly how I did

Syed Hamza Khalid - 3 years, 10 months ago

Hi! Could you please explain how 36c^3 + 33c^2 + 10c + 1 = (3c + 1)^2(4c + 1) works?

Marcus Lidberg - 3 years, 7 months ago

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I have the same question. I noticed in my HP50G that this factorization was possible but it did not know how to get there.

Dênis Silva Oliveira - 4 months, 3 weeks ago
Dinamani Borah
Feb 13, 2015

That style rocks!

Agnishom Chattopadhyay - 6 years, 4 months ago

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I don't know what the downvotes are for, probably they are by people who cannot take pictures in their device, but seriously taking a picture of your solution is so much easier than writing the whole solution in LateX. Though this one does not use LateX, it is certainly less work for other problems.

Soumava Pal - 5 years, 3 months ago

This is a gud way of posting solution

Amartya Anshuman - 6 years, 4 months ago
Dhirendra Singh
Feb 12, 2015

( 1 + a + 2 b + 3 c + 2 a b + 3 a c + 6 b c + 6 a b c ) = 1 + a + 2 b + 2 a b + 3 c + 3 a c + 6 b c + 6 a b c = 1 ( 1 + a ) + 2 b ( 1 + a ) + 3 c ( 1 + a ) + 6 b c ( 1 + a ) = ( 1 + a ) ( 1 + 2 b + 3 c + 6 b c ) = ( 1 + a ) ( 1 ( 1 + 2 b ) + 3 c ( 1 + 2 b ) ) = ( 1 + a ) ( 1 + 3 c ) ( 1 + 2 b ) = 1000 × 1000 × 1333 = 1333000000 (1+a+2b+3c+2ab+3ac+6bc+6abc) \\= 1+a+2b+2ab+3c+3ac+6bc+6abc \\= 1(1+a)+ 2b(1+a) + 3c (1+a) +6bc(1+a) \\= (1+a)(1+2b+3c+6bc) \\= (1+a) (1(1+2b)+3c(1+2b)) \\= (1+a)(1+3c) (1+2b) \\= 1000\times1000\times1333 \\= \boxed{1333000000}

Nikko Quirap
Feb 14, 2015

1 + a +2b + 3c + 2ab + 3ac + 6bc + 6abc

Factor 2b (1 + a) + 3c (1 + a) + (6bc + 1) (1 + a)

(1 + a) (2b + 3c + 6bc + 1)

(1 + a) [2b (3c + 1) + (3c + 1)]

(1 + a) (2b +1) (3c +1)

Then substitute the value of a, b, and c

(1 + 999) [2 (666) +1] [3(333) + 1] = 1 333 000 000

Gamal Sultan
Feb 15, 2015

a = 3c, b = 2c

(1 + a) + (2b + 2ab) + (3c + 3ac) + (6bc + 6abc) =

(a + 1)(1 + 2b + 3c + 6bc) =

(a + 1)(1 +4c + 3c + 12c^2) = (a + 1)(1 +7c + 12c^2) = (a + 1)(1 + 3c)(1 + 4c) =

(a + 1) (a + 1)(1333) = (1000) (1000)(1333) = 1333000000

Tanmay Goyal
Feb 13, 2015

1 + a + 2 b + 3 c + 2 a b + 3 a c + 6 b c + 6 a b c 1+a+2b+3c+2ab+3ac+6bc+6abc

( 1 + a ) + 2 b ( 1 + a ) + 3 c ( 1 + a ) + 6 b c ( 1 + a ) (1+a)+2b(1+a)+3c(1+a)+6bc(1+a)

( 1 + a ) ( 1 + 2 b + 3 c + 6 b c ) (1+a)(1+2b+3c+6bc)

U s i n g , a = 3 c , b = 2 c , c = 333 Using, a=3c,b=2c , c = 333

( 1 + a ) ( 1 + 2 b + a + 2 a b ) (1+a)(1+2b+a+2ab)

( 1 + a ) ( 1 + a ) ( 1 + 2 b ) (1+a)(1+a)(1+2b)

( 1 + a ) ( 1 + a ) ( 1 + a + c ) (1+a)(1+a)(1+a+c) = 1000 1000 1333 = 1333000000 \boxed{1000*1000*1333=1333000000}

Sammy Berger
Feb 13, 2015

a = 3 c, b = 2 c

By substitution,

1 + 3c + 2 * 2c + 3c + 2 * 3c * 2c + 3 * 3c * c + 6 * 2c * c + 6 * 3c * 2c * c

which brings us to

1 + 3c + 4c + 3c + 12c * c + 9c * c + 12c * c + 36c * c * c

and then down to

1 + 10c + 33c * c + 36c * c * c

which I then plugged into a calculator. Not as glorious as factoring, but it got the answer fast enough.

Naman Yadav
Feb 12, 2015

1+a +2b+2ab+3c+3ac+6bc +6abc (1+a)+2b(1+a)+3c(1+a) +6bc(1+a) a=3c and b=2c (1+a)+4c(1+a)+3c(1+a)+12c^2(1+a) (1+a) (12c^2+4c+3c+1) 1000(4c(3c+1)+1(3c+1) ) =1000( (4c+1) (3c+1) ) 1000(1333) (1000) =1333000000

1 + a + 2 b + 3 c + 2 a b + 3 a c + 6 b c + 6 a b c 1+a+2b+3c+2ab+3ac+6bc+6abc

Rearrange as follows:

= 1 + a + 2 b + 2 a b + 3 c + 3 a b + 6 b c + 6 a b c =1+a+2b+2ab+3c+3ab+6bc+6abc

Take common factors among the terms:

= ( 1 + a ) + 2 b ( 1 + a ) + 3 c ( 1 + a ) + 6 b c ( 1 + a ) =(1+a)+2b(1+a)+3c(1+a)+6bc(1+a)

Factorise:

= ( 1 + a ) ( 1 + 2 b + 3 c + 6 b c ) =(1+a)(1+2b+3c+6bc)

= ( 1 + a ) [ 1 ( 1 + 2 b ) + 3 c ( 1 + 2 b ) ] =(1+a)[1(1+2b)+3c(1+2b)]

Group all the factors:

= ( 1 + a ) ( 1 + 2 b ) ( 1 + 3 c ) =(1+a)(1+2b)(1+3c)

Substitute values:

= ( 1 + 999 ) ( 1 + 2 666 ) ( 1 + 3 333 ) =(1+999)(1+2\cdot666)(1+3\cdot333)

Simplify:

= ( 1000 ) ( 1 + 1332 ) ( 1 + 999 ) =(1000)(1+1332)(1+999)

= ( 1000 ) ( 1333 ) ( 1000 ) =(1000)(1333)(1000)

= 1333000000 =\huge\boxed{1333000000}

Excellent! clear description I can follow - except there is a typo in the second line. It should be 3ac, not 3bc.

Diane Sollazzo - 2 years ago
D H
Jul 24, 2016

this is easy

Vignesh .G
Mar 11, 2015

1+a+2b+3c+2ab+3ac+6bc+6abc =1+a+2b+2ab+3c+3ac+6bc+6abc =(1+a)+2b(1+a)+3c(1+a)+6bc(1+a) =(1+a)(1+2b+3c+6bc) =(1+a){(1+2b)+3c(1+2b)} =(1+a)(1+2b)(1+3c) =(1000)(1333)(1000) =1333000000

Asma Rasheed
Feb 23, 2015

(1+a)+2b(1+a)+3c(1+a)+6bc(1+a)

=(1+a)[1+2b+3c+6bc]

=1000[(1+2b)+3c(1+2b)]

=1000[(1+2b)(1+3c)]

=(1000)(1333)(1000)

=1333000000

Gandoff Tan
Apr 23, 2020

= 1 + a + 2 b + 3 c + 2 a b + 3 a c + 6 b c + 6 a b c = ( 1 + a ) + 2 b ( 1 + a ) + 3 c ( 1 + a ) + 6 b c ( 1 + a ) = ( 1 + a ) ( 1 + 2 b + 3 c + 6 b c ) = ( 1 + a ) ( ( 1 + 2 b ) + 3 c ( 1 + 2 b ) ) = ( 1 + a ) ( 1 + 2 b ) ( 1 + 3 c ) = ( 1 + 999 ) ( 1 + 2 ( 666 ) ) ( 1 + 3 ( 333 ) ) = ( 1000 ) ( 1333 ) ( 1000 ) = 1333000000 \begin{aligned} &\phantom{=}1+a+2b+3c+2ab+3ac+6bc+6abc\\ &=(1+a)+2b(1+a)+3c(1+a)+6bc(1+a)\\ &=(1+a)(1+2b+3c+6bc)\\ &=(1+a)((1+2b)+3c(1+2b))\\ &=(1+a)(1+2b)(1+3c)\\ &=(1+999)(1+2(666))(1+3(333))\\ &=(1000)(1333)(1000)\\ &=\boxed{1333000000} \end{aligned}

Oon Han
Jul 7, 2019

We can rearrange the terms in the expression to make it easier to factorise. 1 + a + 2 b + 3 c + 2 a b + 3 a c + 6 b c + 6 a b c = 6 a b c + 2 a b + 3 a c + a + 6 b c + 2 b + 3 c + 1 = 2 a b ( 3 c + 1 ) + a ( 3 c + 1 ) + 2 b ( 3 c + 1 ) + 3 c + 1 = ( 2 a b + a + 2 b + 1 ) ( 3 c + 1 ) = ( a ( 2 b + 1 ) + 2 b + 1 ) ( 3 c + 1 ) = ( a + 1 ) ( 2 b + 1 ) ( 3 c + 1 ) \begin{aligned} 1 + a + 2b + 3c + 2ab + 3ac + 6bc + 6abc &= 6abc + 2ab + 3ac + a + 6bc + 2b + 3c + 1 \\ &= 2ab(3c + 1) + a(3c + 1) + 2b(3c + 1) + 3c + 1 \\ &= (2ab + a + 2b + 1)(3c + 1) \\ &= \left(a(2b + 1) + 2b + 1)(3c + 1\right) \\ &= (a + 1)(2b + 1)(3c + 1) \end{aligned} Then, substituting the values a = 999 \textcolor{#D61F06}{a = 999} , b = 666 \textcolor{#3D99F6}{b = 666} and c = 333 \textcolor{#20A900}{c = 333} gives: ( a + 1 ) ( 2 b + 1 ) ( 3 c + 1 ) = ( 999 + 1 ) ( 2 ( 666 ) + 1 ) ( 3 ( 333 ) + 1 ) = ( 1000 ) ( 1333 ) ( 1000 ) = 1333000000 \begin{aligned} (a + 1)(2b + 1)(3c + 1) &= (999 + 1)\left(2(666) + 1\right)\left(3(333) + 1\right) \\ &= (1000)(1333)(1000) \\ &= \boxed{1333000000} \end{aligned} Thus, the answer is 1333000000 .

Gary Munnelly
Dec 5, 2018

1 + a + 2 b + 3 c + 2 a b + 3 a c + 6 b c + 6 a b c 1+a+2b+3c+2ab+3ac+6bc+6abc

Group all parts that are multiplied by c c

1 + a + 2 b + 2 a b + ( 3 c + 3 a c + 6 b c + 6 a b c ) 1+a+2b+2ab+(3c+3ac+6bc+6abc)

Factor out 3 c 3c

1 + a + 2 b + 2 a b + 3 c ( 1 + a + 2 b + 2 a b ) 1+a+2b+2ab+3c(1+a+2b+2ab)

Now simplify 1 + a + 2 b + 2 a b 1+a+2b+2ab :

( a + 1 ) ( 2 b + 1 ) + 3 c ( a + 1 ) ( 2 b + 1 ) (a+1)(2b+1)+3c(a+1)(2b+1)

Factor out ( a + 1 ) ( 2 b + 1 ) (a+1)(2b+1)

( a + 1 ) ( 2 b + 1 ) ( 3 c + 1 ) (a+1)(2b+1)(3c + 1)

Now just introduce the values for a, b and c then solve:

( 999 + 1 ) ( 2 ( 666 ) + 1 ) ( 3 ( 333 ) + 1 ) (999+1)(2(666)+1)(3(333) + 1)

( 1000 ) ( 1333 ) ( 1000 ) (1000)(1333)(1000)

1333000000 1333000000

Ismat Ara
Oct 26, 2018

Ong Zi Qian
Feb 5, 2017

The question is easy, since 1+a+2b+3c+2ab+3ac+6bc+6abc =(a+1)(2b+1)(3c+1) =(999+1)(2 666+1)(3 333+1) =1000x1333x1000 =1333000000

Chenjia Lin
Jul 31, 2016

First, group the terms by their coefficients.

( a + 1 ) + ( 2 b + 2 a b ) + ( 3 c + 3 a c ) + ( 6 b c + 6 a b c ) (a+1)+(2b+2ab)+(3c+3ac)+(6bc+6abc)

Next, factor a GCD from each set of parentheses.

( a + 1 ) + 2 b ( a + 1 ) + 3 c ( 1 + a ) + 6 b c ( a + 1 ) (a+1)+2b(a+1)+3c(1+a)+6bc(a+1)

Since a + 1 a+1 is common in each of the terms, we can factor it out, which leaves:

( a + 1 ) ( 1 + 2 b + 3 c + 6 b c ) (a+1)(1+2b+3c+6bc)

Looking back at the values for a, b, and c, we can write b b as 2 c 2c and a a as 3 c 3c .

( 3 c + 1 ) ( 1 + 4 c + 3 c + 12 c 2 ) (3c+1)(1+4c+3c+12c^2)

= ( 3 c + 1 ) ( 12 c 2 + 7 c + 1 ) =(3c+1)(12c^2 + 7c +1)

= ( 3 c + 1 ) ( 4 c + 1 ) ( 3 c + 1 ) =(3c+1)(4c+1)(3c+1)

= ( 3 c + 1 ) 2 ( 4 c + 1 ) =(3c+1)^{2}(4c+1)

Finally, we plug in 333 for c, and we get 3 c + 1 = 1 , 000 , 000 3c+1=1,000,000 and 4 c + 1 = 1333 4c+1=1333 . Multiplying 1,000,000 and 1333 together, we get 1 , 333 , 000 , 000 \boxed{1,333,000,000} .

Kamran Rasheed
Jun 24, 2016

=(1+a)+2b(1+a)+3c(1+a)+6bc(1+a) =(1+a)(1+2b+3c+6bc) =(1+a){1+2b+3c(1+2b)} =(1+a)(1+2b)(1+3c) =1000(1333)(1000) =1333000000

Alan Chen
Jan 17, 2016

The answer is 1,333,000,000 - and the funny thing is, somewhere in my calculations I made an error, and I got 1,332,999,000

Venkatesh P
Jan 2, 2016

it easy but due to calculation errors one can get it right for third time.

Dodo Ashraf
Feb 15, 2015

a=3c and b=2c

then 1+a+2b+3c+2ab+3ac+6bc+6abc will be equal to

1+3c+4c+3c+12c c+9c c+12c c+36c c*c

=1+7c+33c^2+36c^3

=1+7(333)+33(333)(333)+36(333)(333)(333)=1333000000

Its actually not 7c but 10c in the last step I don't know how come u have arrived at thisanswer

r j - 6 years, 3 months ago
Sayma Hasan Kheya
Feb 14, 2015

1+a+2b+3c+2ab+3ac+6bc+6abc =1+a+2b+2ab+3c+3ac+6bc+6abc =(1+a)+2b(1+a)+3c(1+a)+6bc(1+a) =(1+a)(1+2b+3c+6bc) =(1+a){(1+2b)+3c(1+2b)} =(1+a)(1+2b)(1+3c) =(1000)(1333)(1000) =1333000000

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