2012 CEMC Gauss (Grade 7) Problems/Problem 6

Problem

Fifteen times a number equals three hundred. The number is

$\text{ (A) }\ 20 \qquad\text{ (B) }\ 10 \qquad\text{ (C) }\ 60 \qquad\text{ (D) }\ 30 \qquad\text{ (E) }\ 25$

Let $n$ be the number that we want to solve for. Setting up an equation, we have:

$15n = 300$

Solving for n, we get:

$n = \frac{300}{15} = \boxed {\textbf {(A) } 20}$

We can use the answer choices to see what the answer is. To do this, we can use $25$ first, and check if the number is too high.

$25 * 15 = 375$

This is more than $300$ , so the answer must be less than $25$ .

We can then try $20$ :

$20 * 15 = 300$

This is equal to $300$ , so the number is $\boxed {\textbf {(A) } 20}$ .