Mistakes give rise to Problems- 12

Algebra Level 5

If you do the following thing in Maths \color{#3D99F6}{\textbf{Maths}} , a ( b c ) = ( a b ) c \displaystyle a^{(b^c )} = ( a^b ) ^c then it will be a Big Mistake !!! \color{#D61F06}{\textbf{Big Mistake !!!}}


But for how many triples of integers ( a , b , c ) \color{#3D99F6}{(a,b,c)} such that 0 a 10 0\leq a \leq 10 and 0 < b , c 10 0 < b,c \leq 10 , is the above said "False" property seen to be "true" ?


This problem is a part of my set Mistakes Give Rise to Problems .


The answer is 299.

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1 solution

Aditya Raut
Jul 31, 2014

Actually problem is to find solutions of a b c = a b c \displaystyle a^{b^{c}}= a^{bc}

We break this in 3 cases, (i) a = 0 a=0 , (ii) a = 1 a=1 and (iii) a [ 2 , 10 ] a\in [2,10]

(i) a = 0 a=0 , the case is true for all permitted ( b , c ) (b,c) , giving 100 100 triples ( a , b , c ) (a,b,c)

(ii) a = 1 a=1 , the case is true for all permitted ( b , c ) (b,c) giving 100 100 triples ( a , b , c ) (a,b,c)

(iii) a [ 2 , 10 ] a\in [2,10] , we have the case b c = b c b^c=bc and this is true if c = 1 c=1 , giving 10 10 pairs ( b , c ) (b,c) and a a has 9 choices, gives 90 90 triples ( a , b , c ) (a,b,c)

If c 1 c\neq 1 , only and only case is b = c = 2 b=c=2 where we get 2 2 = 2 × 2 = 4 2^2=2\times 2=4 again, a a has 9 choices, giving 9 9 triples ( a , b , c ) (a,b,c)

So as a whole there are 100 + 100 + 90 + 9 = 299 100+100+90+9= \boxed{299} triples following needed thing.

oh no i did not consider the 90 triplet case.

prashant goyal - 6 years, 10 months ago

I'm trying to guess why it's exactly 1 less that 300....

Satvik Golechha - 6 years, 10 months ago

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LOL that 1 TRIPLE ( 0 , 0 , 0 ) (0,0,0) made this happen, it's because 0 0 0^0 is not defined.

Aditya Raut - 6 years, 10 months ago

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0 0 = 1 0^{0}=1

Anoorag Nayak - 5 years, 5 months ago

in 2nd case ie a = 1 , 2 cases occur i) b=0 and c can have 10 values except 0 and ii) when b assumes the other 10 values and can have 11 values so the 2nd case total becomes 120 .Correct me if i am wrong

sama nag - 6 years, 10 months ago

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b b can't be 0 0 because see what is the given range, there is strict inequality at 0 < b , c 10 0<b,c\leq 10 . So you can't take b or c to be 0.

Aditya Raut - 6 years, 10 months ago

Good problem, I missed the 9 triples and got 290

Pankaj Joshi - 6 years, 10 months ago

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Lol. I had the answer right in front of my eye, and I didn't count the last 8 triples...

Nick Lee - 6 years, 9 months ago

same way! nice problem

Ashu Dablo - 6 years, 8 months ago

I have a question: The 3 restrictions are :

                                        0<=a<=10


                                        0<b


                                       C<=10

Under these conditions "bc" and "b^c" are always real numbers

And 1 to any real power is 1

There are also infinite combos of b and c

So how does your solution assume that b and c both only have 10 possible numbers to choose from?

Please explain what detail I am missing?

Maninder Dhanauta - 5 years, 4 months ago

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They are integers!

Ashu Dablo - 5 years, 3 months ago

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