Perfect Square Product

How many positive integers less than 1000 1000 yields a perfect square number when multiplied by 792 792 ?


The answer is 6.

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11 solutions

Doug Boyd
Dec 22, 2013

The prime factorization of 792 = 3 2 2 3 11 792 = 3^2 * 2^3 * 11 , or in more useful terms, 3 2 2 2 2 11 3^2 * 2^2 * 2 * 11 . Since the 3 2 3^2 and 2 2 2^2 are already perfect squares, we just need to multiply by something with another 2 2 and another 11 11 in it. 22 22 is an obvious choice, and is the first solution. Any other multiple of 22 22 with a perfect square would work as well. So 22 4 , 22 9 , 22 16 , 22 25 22*4, 22*9, 22*16, 22*25 , and 22 36 22*36 are also solutions. 22 49 22*49 is larger than 1000 1000 , so we must stop with 36 36 .

The solutions are 22 , 88 , 198 , 352 , 550 22, 88, 198, 352, 550 , and 792 792 for a total of 6 6 .

oops.......i got the above listed 6 nos. and i also 176 by mistake

Ganesh Ayyappan - 7 years, 4 months ago
Ajay Maity
Dec 22, 2013

From the question, we can say that any positive integer multiplied with 792 792 must yield a perfect square.

i.e. Let's say x × 792 x \times 792 is a perfect square.

Find all the factors of 792, we get

x × 4 × 9 × 11 × 2 x \times 4 \times 9 \times 11 \times 2 must be a perfect square.

Here, 4 4 and 9 9 are already squares, but 11 11 and 2 2 are not. So, in order that the above quantity is a perfect square, x x must contain the term 11 × 2 11 \times 2 in it.

So, x x contains 11 × 2 × 11 \times 2 \times something . Note that something must be a perfect square.

So, we put different squares starting from 1, 4, 9, 16, ... and calculate 11 × 2 × 1 11 \times 2 \times 1 , 11 × 2 × 4 11 \times 2 \times 4 ..... This quantity must be less than 1000.

We see that 11 × 2 × 1 11 \times 2 \times 1 , 11 × 2 × 4 11 \times 2 \times 4 , .... 11 × 2 × 36 11 \times 2 \times 36 are all less than 1000. But 11 × 2 × 49 11 \times 2 \times 49 is not.

Hence, there are 6 6 possible values.

That's the answer!

That's exactly what I did ! Upvoted you !

Priyansh Sangule - 7 years, 3 months ago
Hahn Lheem
Dec 22, 2013

The prime factorization of 792 792 is 2 3 3 2 11 2^3 \cdot 3^2 \cdot 11 . A perfect square is a number where all of the exponents of all prime factors is even. Therefore, the positive integers that satisfy is in the form 22 k 2 22k^2 , where k k is any positive integer. The range that k k can be in in order for 22 k 2 22k^2 to be less than 1000 1000 is [ 1 , 6 ] [1,6] , so there are 6 \boxed{6} possible integers.

Soham Zemse
Dec 22, 2013

792 factors as 2 x 2 x 2 x 3 x 3 x 11.

we strictly need a "2" and a "11" to make it a perfect square.

so the simplest, we can multiply " 22 " to 792 for makeing a perfect square.

" a perfect square x 22 " x 792. is a perfect square.

so we can multiply 22 with 1,4,9,…. and the number should be less than 1000.

that happens with only upto 36.

so the numbers are 22 x 1, 22 x 4, 22 x 9, 22 x 16, 22 x 25 and 22 x 36.

there are 6 numbers that we want

Well, 792 = 2 2 2 3 3 11 792 = 2\cdot 2\cdot 2\cdot 3\cdot 3\cdot 11 . Then, any number multiplying this needs to multiply 2 11 2 \cdot 11 , because we need to have an even quantity of each prime factor. Then, 2 11 2 \cdot 11 needs to be multiplied by an even quantity of factors.

Note that 2 11 7 7 = 1078 2 \cdot 11 \cdot 7 \cdot 7 = 1078 . Hence, the prime factors that we can add up are 2 2 , 3 3 and/or 5 5 . Then, note that 2 11 5 5 = 550 2\cdot11\cdot5\cdot5 = 550 . Then, the pair of 5 5 's will not be accompanied by another pair (because then the number will be greater than 1000 1000 ). We continue with the 3 3 's. 2 11 3 3 = 198 2\cdot11\cdot3\cdot3 = 198 . In this case we can only add up a pair of 2 2 's. Then, with the 2 2 's, we have 2 11 2 2 2\cdot11\cdot2\cdot2 and 2 11 2 2 2 2 2\cdot11\cdot2\cdot2\cdot2\cdot2 . So, let's list below, and formally, all the possible numbers:

2 11 2\cdot11

2 11 2 2 2\cdot11\cdot2\cdot2

2 11 2 2 3 3 2\cdot11\cdot2\cdot2\cdot3\cdot3

2 11 2 2 2 2 2\cdot11\cdot2\cdot2\cdot2\cdot2

2 11 3 3 2\cdot11\cdot3\cdot3

2 11 5 5 2\cdot11\cdot5\cdot5

Finally, the answer is 6 \boxed {6} .

Siddharth Tiwari
Aug 10, 2014

792 can be written as 2^3 * 3^2 * 11, so first requirement is to get the already present factors in 792 to be perfect square, so the least number which is required is 2*11 i.e. 22, now we know that only multiple of 22 can satisfy the condition, so apart from 22 other multiples should be having the perfect square terms, so 22 * 4 , 22 * 9, 22 * 16, 22 * 25, 22 * 36. after this the number will be greater than 1000, so correct answer is 6..

First, take note that 792 = 8 9 11 = 2 3 3 2 11 792 = 8*9*11 = 2^{3}*3^{2}*11 . Thus, the smallest number we must have to multiply by 792 in order to produce a square number is 2 11 = 22 2*11 = 22 . Next, we must find the multiples of 22 which are of the form 22 n 2 22*n^{2} . Noticing that 22 45 = 990 22*45 = 990 and 22 46 = 1012 22*46 = 1012 , n 2 n^{2} must then be less than or equal 45. Thus, n n can assume one of the following values: (1, 2, 3, 4, 5, 6). Numbers from 7 onward are ruled out since 7 2 = 49 > 45 7^{2} = 49 > 45 , thus we only have 6 numbers that satisfy the problem.

Mohamed Laghlal
Jan 2, 2014

La decomposition en facteur premier de 792 est 2^3 3^2 11 , pour qu'un carree soit parfait il faut que touts ses nombres premiers (decomposeurs) aillent soit des carrees donc ayant des puissances paires ainsi on remarque que pour que 792 soit carree il faut le multiplier par 2 11 (en le multipliant par ce nombre toutes les puissances des nombres premiers deviennent paires) , et le nombre des multiples par carrees (cad 22 multiplie par 1, 4, 9...) inferieurs a 1000 est le nombre cherché. 22 (6^2) = 792 et 22*(7^2) = 1078. Donc le nombre d'entiers positifs qui sont inferieurs a 1000 et representent un carree l'orsqu'on les mutiplie par 792 est \boxed{6}.

La decomposition est 2^{3) \times 3^{2} \times 11 , et le quatriemme nombre est 2 \times 11. Je ne suis pas encore habitue a Latex.

Mohamed Laghlal - 7 years, 5 months ago
Jason Sebastian
Dec 31, 2013

792 792 can be factorized into 2 3 . 3 2 . 11 2^3.3^2.11 . So, the smallest positive integer which yields a perfect square number when multiplied by 792 792 is 22 22 . Since 792 22 792*22 is a perfect square number, when multiplied to any perfect square number, it will remain a perfect square number. They are 22 1 , 22 4 , 22 9 , 22 16 , 22 25 22*1, 22*4, 22*9, 22*16, 22*25 and 22 36 22*36 . 6 \boxed{6} is the answer.

factorize 792. By factorizing 792 we get the following : 2x2 x 3x3 x 2x11. now if we multiply 2X11 that is 22 with 792 we get: 2x2 x 3X3 x 2X11 x 2x11 which is a perfect square .. Now to get more perfect squares we can go on multiplying perfect squares with this no..like 4,9,16... taking care that 2x11x(the perfect square) doesn't exceed 1000.. so up to how many squares can we multiply?? divide 1000 by 22, we get 45.45.. so 22X45 is just below 1000, multiplying anything above 45 with 22 will take the product over 1000.. so we can multiply perfect squares upto 45 with 22 and multiply that product with 792..

so the numbers are: 22 X 1=22 ( this is in fact the first number i have calculated) 22 X 4=88 22 X 9=198 22 X 16=352 22 X 25=550 22 X 36=792...

Budi Utomo
Dec 22, 2013

We must know if 792 = 2^3 . 3^2 . 11, So, positive integers less than 1000 yields a perfect square number when multiplied by 792 are 2^1.11 , 2^3 . 11 , 2^5 . 11 , 3^2 . 11 , 3^4.11 , and 2^1 . 3^2 . 11. There are 6 positive integers. Answer : 6

This solution is wrong. For example, 3^4.11 is not an answer. The 6 answers are 22x1, 22x4, 22x9, 22x16, 22x25 and 22x36.

Tong Choo - 7 years, 5 months ago

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As Tong Choo said, both 3 4 × 11 3^4\times 11 and 3 2 × 11 3^2\times 11 are incorrect.

Vincent Tandya - 7 years, 5 months ago

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