Testing testing 2, 34, 56

For how many integers N N from 1 to 1000 (inclusive) is

2 N + 34 2N + 34

a multiple of 56?

Note: You may use the fact that 1000 = 17 × 56 + 48 1000 = 17 \times 56 + 48 .


The answer is 36.

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17 solutions

Kishlaya Jaiswal
Nov 4, 2013

Let 2 N + 34 = 56 k 2N + 34 = 56k

Then N = 28 k 17 N = 28k - 17

Now,

k N 0 17 1 11 2 39 36 991 37 1019 \begin{array}{c|c} k & N \\ \hline 0 & -17 \\ 1 & 11 \\ 2 & 39 \\ \ldots & \ldots \\ 36 & 991 \\ 37 & 1019 \\ \hline \end{array}

Since 1 N 1000 1 k 36 1 \leq N \leq 1000 \Rightarrow 1 \leq k \leq 36

Therefore, there are only 36 \boxed{36} possible values for N

indians are indians

santhosh sivan - 7 years, 7 months ago

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what do you mean by that ???

Kishlaya Jaiswal - 7 years, 7 months ago

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Every Indian is intelligent

Ewerton Cassiano - 7 years, 7 months ago

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@Ewerton Cassiano For that matter, every human possesses intelligence.

Tanishq Aggarwal - 7 years, 7 months ago

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@Tanishq Aggarwal Doubtlessly, every human is intelligent. Need not be Math.

A Brilliant Member - 7 years, 7 months ago

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@A Brilliant Member Completely agreed... Typo : every human is talented (more suitable)

Kishlaya Jaiswal - 7 years, 7 months ago

Nice solution

Shriniwas Kumar - 7 years, 7 months ago

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Thnx....

Kishlaya Jaiswal - 7 years, 7 months ago

easy solution

Pooja varadarajan - 7 years, 7 months ago

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Thnx

Kishlaya Jaiswal - 7 years, 7 months ago

How did you render that table in LaTeX?

A Former Brilliant Member - 7 years, 7 months ago

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Yes... :)

Kishlaya Jaiswal - 7 years, 7 months ago

OMG! Very nice solution,good job =D

Willie Zhi Jie Zhang - 7 years, 7 months ago

Beautiful.

Ben Haffner - 7 years, 7 months ago

just the same way like mine...

Heri Fauzan - 7 years, 7 months ago

thats RIGHT INDIAN = SMARTTTTT

Harshil Parikh - 7 years, 7 months ago
Snehdeep Arora
Nov 4, 2013

Note that 2 N + 34 2N+34 is even and every multiple of 56 is also even.This means that every multiple of 56 will give us an integer value of N.We see that for N = 1000 , 2 N + 34 = 2034 N=1000 , 2N+34 =2034 and 2034 18 ( m o d 56 ) 2034\equiv 18 \pmod{56} .

\Rightarrow 2034 18 = 2016 2034-18=2016 gives us an integer value of N(which is 991).Also 2016 = 56 × 36 2016=56 \times {36} .Which means that every multiple of 56 up to 2016 gives us an integer value of N less than 1000.

Total values of N=36.

This is the easiest solution I found. Nice one.

Ashwin Singh - 7 years, 7 months ago
Daniel Chiu
Nov 3, 2013

Clearly, n = 11 n=11 works. Then, solutions for N N must differ by at least 28 28 , and 2 ( 11 + 28 n ) + 34 = 22 + 34 + 56 n = 56 ( n + 1 ) 2(11+28n)+34=22+34+56n=56(n+1) Therefore, all values N 11 ( m o d 2 ) 8 N\equiv 11\pmod 28 work. There are 36 \boxed{36} values.

I got a intuitive Solution 2 N + 34 = 2 ( n + 17 ) 2N+34=2(n+17)

n + 17 n+17 must be divisible by 28 28

lets Write n is the form 17 + x 28 -17+x28

Clearly X varies from 1 1 to 36 36 .Thus Answer is 36 \boxed{ 36 }

Pratyush Agarwal - 7 years, 7 months ago
敬全 钟
Nov 4, 2013

The given expression can be factorized as

2 N + 34 2N+34 = = 2 ( N + 17 2(N+17 )

Since 56 56 = = 2 3 × 7 2^{3} \times 7 , therefore, N + 17 N+17 must be a multiple of 28 28 .

Then, the given fact can be rewritten as follows.

1000 1000 = = 17 × 56 + 48 17 \times 56 + 48

1000 1000 = = 17 × 28 × 2 + 48 17 \times 28 \times 2 +48

1000 1000 = = 34 × 28 + 20 + 28 34 \times 28 +20 +28

1000 1000 = = 35 × 28 + 20 35 \times 28 +20

Therefore we can say that there are 35 35 multiples of 28 28 from 1 1 to 1000 1000 (inclusive).

But we also know that 36 × 28 11 36 \times 28 - 11 is smaller than 1000 1000 . Therefore, there are 35 + 1 35 + 1 = = 36 36 integers that satisfy the integers N N .

Note that k , N such that 2 N + 34 = 56 k \forall k, \exists N \text{ such that } 2N+34=56k . Hence, our solution is simply: 2 ( 1000 ) + 34 ( 2 ( 1 ) + 34 ) 56 + 1 = 36 \left \lfloor \frac{2(1000)+34-(2(1)+34)}{56} \right \rfloor + 1=36

Tanishq Aggarwal
Nov 7, 2013

We have that 2 N + 34 0 ( m o d 56 ) 2N+34 \equiv 0 \pmod {56} N + 17 0 ( m o d 28 ) N+17 \equiv 0 \pmod {28} N 9 ( m o d 28 ) N \equiv 9 \pmod {28} This means we can write N = 28 k + 9 N=28k+9 for integers k. We have that 28 k + 9 1000 28k+9 \leq 1000 , so 28 k 991 28k \leq 991 , so k 35 k \leq 35 . k k can be anything from 0 to 35, so there are 36 possible values of k k , and thus 36 \boxed{36} possible values of N N .

Nice, and simple! Well done!😎

Prem Chebrolu - 2 years, 9 months ago
Shaun Loong
Nov 3, 2013

When N = 1000 , 2 N + 34 = 2034 N=1000, 2N+34=2034 . Therefore, 2034 56 = 36 \lfloor \frac{2034}{56}\rfloor = \boxed{36} Why is this so? The floor function shows that within 2034 2034 , 36 36 values are divisible by 56 56 .

NOTE when N = 1 N=1 , 2 N + 34 = 36 2N+34=36 (not a multiple of 56 56 ). It is important to check the range of N N .

Alan Li
Nov 7, 2013

We know that we can form any integer that is a multiple of 56 with that given, because 2N has to be even, and you are adding 34, another even number

The largest number we can form where N is less than 1000 that is a multiple of 56 is 2016.

We then divide 2016 by 56 to find the amount of multiples of 56 that are less than 2016

2016/56=36

There are 36 possibilities for N

Ant6880 C
Nov 7, 2013

First, I solved the equation for 1000. This equaled 2034. Then I calculated all the multiples of 56 under 2034. There were 36 of them. I knew that if I plugged the 36 multiples of 56 I found as the answer to the equation, and I solved for N for all the different equations, N could equal 36 different things. So, 36 is the answer.

Rui-Xian Siew
Nov 6, 2013

Let 2N+34=56a.

N=28a-17. Since N is between 1 and 1000 when a=1 until a=36, there are 36 a which satisfies the condition.

Ayon Pal
Nov 6, 2013

There 2 N + 34 = 56 N = 11 2N + 34 = 56 \implies N = 11

Then 2 N + 34 = 56 × 2 = 112 N = 39 2N + 34 = 56 \times 2 = 112 \implies N = 39

2 N + 34 = 56 × 3 = 168 N = 67 2N + 34 = 56 \times 3 = 168 \implies N = 67

2 N + 34 = 56 × 4 = 224 N = 95 2N + 34 = 56 \times 4 = 224 \implies N = 95

So, We get a sequence 11 , 39 , 67 , 95 , 123... 11, 39, 67, 95, 123 ... [Which is increasing by 28]

And there is 1000 / 28 = 35 1000 / 28 = 35 numbers in the sequence.

And the 1st one is 11 11

So, There is 35 + 1 = 36 35 + 1 = \boxed{36} integer value of N N

Nice resolution !

Guilherme Naziozeno - 7 years, 7 months ago

Using modular arithmetic, we want to find N N between 1 1 and 1000 1000 , such that 2 N + 34 mod 56 = 0 2N+34 \ \text{mod}\ 56=0 . The first integer satisfying this is 11 11 , and there are then 1000 11 = 989 1000-11=989 integers left. Since 2 28 = 56 2\cdot 28=56 , the next N N 's to satisfy the equation will be 11 11 plus a multiple of 28 28 . The number of such N 1000 N\leq 1000 is found by 989 28 = 35. \lfloor \displaystyle\frac{989}{28}\rfloor=35. So the total number of N N is the 11 11 and the multiples of 28 28 : 1 + 35 = 36 1+35=36

Paola Ramírez
Apr 19, 2014

2 N + 34 = 56 2N+34=56 so N + 17 = 28 N 11 m o d 28 N+17=28 \Rightarrow N \equiv 11 mod 28 that it's equal to 28 n 11 = N 28n-11=N

28 n 11 = 1000 n = 36 28n-11=1000 \Rightarrow n= 36

2N+34=56a so 2N=56a-34 so N={56a-34}/2 since N is <or =1000 so, 56a-34< or = 2000 a is ,or = 36.32 Clearly a= \boxed {36}

mistake sorry..................

ashutosh mahapatra - 7 years, 1 month ago
Sahil Gohan
Apr 5, 2014

2N + 34 = 56a

N = 28a - 17

we also know that N is between 1 to 1000 ( inclusive)

therefore to keep N in that range a can only take values from 1 to 36. hence giving us a total of 36 values

Ojas Jain
Nov 9, 2013

GIVEN,N=1-1000 THEREFORE,2N+34=36-2034 BUT,MULTIPLES OF 56 ARE-56,112,168... THEREFORE,MAXIMUM MULTIPLE OF 56 WILL BE LESS THAN OR EQUAL TO 2034 THEREFORE,t<2034 56+[n-1]56<2034 56n<2034 n<2034/56 n<36....THEREFORE n=36

David Kroell
Nov 9, 2013

I programmed it:

    int y = 0;

   for (int x = 1; x < 1001; x++) {
       int z = 2*x + 34;
       if (z % 56 == 0) {
           y += 1;
       }
    }
   System.out.println("The number of multiples is: " + y);

Yeah, so I cheated a little bit. ;)

counter = 0

for x in range(1000):
    z = 2*x+34
    if z % 56 == 0:
        counter +=1
print("The answer is ", str(counter) + ".")
(In Python)

William Cui - 7 years, 7 months ago

Hoho, me too !

Dim b As Integer
Dim c As Integer
Dim d As Integer
Do While c < 1001
        c = c + 1
        b = 2 * c + 34
        If b Mod 56 = 0 Then
            d = d + 1
        End If
    Loop
    MessageBox.Show(d)
Guilherme Naziozeno - 7 years, 7 months ago

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What language? Mine is Java.

David Kroell - 7 years, 7 months ago

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Visual basic

Guilherme Naziozeno - 7 years, 7 months ago

Nice to see we have some fellow programmers.

David Kroell - 7 years, 6 months ago

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