Practice: Finding common multiples

How many positive integers less than or equal to 1000 1000 are common multiples of the three numbers 8 , 36 , 8, 36, and 24 24 ?

14 13 12 11

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16 solutions

The least common multiple is 72. hence 1000 divided by 72 comes to 13.

Evan Bergeron
Dec 19, 2013

8's prime factorization is 2,2,2. 36's prime factorization is 2,2,3,3. 24's prime factorization is 2,2,2,3.

A common multiple of all three of these numbers will be divisible by their least common multiple. That is, each of our numbers will need to have a prime factorization that consists of at least 3 2's (as 24 has 3 2's) and 2 3's (as 36 has 2 3's).

In other words, each of our numbers will need to be divisible by 2(2)(2)(3)(3) = 72.

Take the floor of 1000/72 and you get 13!

The least common multiple of 8, 24 and 36 is 72 .

8 = 2 3 8 = 2^{3}

24 = 2 3 × 3 24 = 2^{3} \times 3

36 = 2 2 × 3 2 36 = 2^{2} \times 3^{2}

L C M = 2 3 × 3 2 = 72 LCM = 2^{3} \times 3^{2} = 72

Hence the common multiples of 8,24, and 36 are multiples of 72. Dividing 1000 by 72, we get 13 with the remainder 64.

13 is the answer.

Awesome!

Ícaro Magalhães - 7 years, 5 months ago
Israel Smith
Dec 20, 2013

1000/lcm(8,36,24)

Ajesh K.C
Dec 19, 2013

LCM of 8,36 and 24 =72 solve using the formula an=a+(n-1)d where a=72, d=72 and an=936. solving we get n=13 which is the required number

Changming Xu
Dec 19, 2013

The LCM of 8 , 36 , 24 8, 36, 24 is 72. Therefore, our answer is the floor of 1000 72 = 13 \frac{1000}{72} = \boxed{13}

Ritwik Verma
Dec 19, 2013

LCM of 8,24,36= 72 thus, all multiples of 72 less than 1000 would also be the multiples of 8, 24 and 36 Hence, first 13 multiples of 72 would be the answer.

S W
Apr 21, 2014

By Calculating least common multiplier is 72 , and 1000/72 is 13.

Anzar Aznzar
Mar 29, 2014

1000 / 72 = 13,88....

x = 13

Mahendra Mete
Mar 13, 2014

common multiple of 8,36,and 24 is 72. 72 has 13 multiple up to 1000

Sunil Pradhan
Feb 9, 2014

The numbers are multiples of 72 which is LCM of 8, 36, 24

1000 ÷ 72 quotient is 13 numbers are multiple of three numbers 8,36, and 24.

Mohammad Fiyaz
Jan 24, 2014

Lowest Common Multiple of 8,36 and 24 is 72. we know that all the multiple of 72 would also be multiple of 8, 36 and 24

thus 1000/72=13(only positive integers)

First integer is 72. 1000/72=13.88. As less than or equal to 1000, the answer is 13.

Muhammad Usman
Jan 14, 2014

take LCM of all Digits and Divide 1000/LCM

Sawrabh Sourabh
Jan 9, 2014

take LCM of 8,36,24. LCM= 72 divide 1000 by 72 neglect the decimal portion.

Sai Prasanth
Dec 22, 2013

first calculate the GCD of (8,36,24) GCD calculation : 8-2^3 ;36-2^2 3^2; 24-2^3 3 and take the highest prime powers in each integer that is 2^3*3^2=72 then find 1000/72 neglect the remainder then the result is 13

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