iNumbv wrote:
It is known that no more than 7 children will be attending a party. What is the smallest number of cookies that must be brought to the party so that each child receives the same number of cookies?
A. 35
B. 105
C. 180
D. 210
E. 420
** Can someone please explain to me the intuition behind this answer? I figure it's a very straightforward answer, but what I don't understand is assuming the maximum number of children attend the party which is 7 and among the answers 35 looks to suffice as each child will receive 5 cookies, which makes it the smallest number among the answers. I'm a bit confused can someone point me to the right direction, Thanks. **
Since the number of cookies must be divisible by 1, 2, 3, 4, 5, 6, and 7, let's find the least common multiple of the integers 1, 2, 3, 4, 5, 6, and 7. Every integer is divisible by 1. Let's find the prime factorizations of 2, 3, 4, 5, 6, and 7.
So we want to find the least common multiple of these integers, which we will write in a column.
The largest number of times the prime factor 2 appears in any of these integers is 2, in . The largest number of times the prime factor 3 appears in any of these integers is 1. Similarly, the largest number of times the prime factors 5 appears in any of these integers is 1, and the largest number of times the prime factors 7 appears in any of these integers is 1.
So the least common multiple of the first 7 positive integers must contain 2 prime factors of 2, 1 prime factor of 3, 1 prime factor of 5, and 1 prime factor of 7.
The least common multiple of the first 7 positive integers is 2 × 2 × 3 × 5 × 7 = 420.
The smallest number of cookies that must be brought to the party is 420, choice (E).
Given: It is known that no more than 7 children will be attending a party.
Asked: What is the smallest number of cookies that must be brought to the party so that each child receives the same number of cookies?
Prime factorisation of 1,2,3,4,5,6,7
1 = 1
2 = 2
3 = 3
4= 2^2
5 = 5
6 = 2*3
7 = 7
Since we don't know the exact number of children attending the party, we have to bring number of cookies which will be equally divided irrespective of number of children attending the party. Number of children = {1,2,3,4,5,6,7}
2^2*3*5*7 = 420
Now the cookies can be divided equally among children irrespective of number of children attending the party.
IMO E