# 20 multiplied by a number, decreased by 15 equals 25. How do you find the number?

Jan 13, 2017

See full explanation for finding the number below

#### Explanation:

To solve this world problem we will convert it to a math problem to solve one phrase at a time.

"by a number" - let's call the number $n$.

"20 multiplied by a number" or by $n$ can be written as:

$20 \times n$ or $20 \cdot n$ or what we will use $20 n$

"decreased by" means to subtract what follows which in this case is "15" so we can expand what we are writing to:

$20 n - 15$

"equals 25" is the same as $= 25$ so we can add this to our expression to get our equation:

$20 n - 15 = 25$

We can now solve:

$20 n - 15 + \textcolor{red}{15} = 25 + \textcolor{red}{15}$

$20 n - 0 = 40$

$20 n = 40$

$20 \frac{n}{\textcolor{red}{20}} = \frac{40}{\textcolor{red}{20}}$

$\textcolor{red}{\cancel{\textcolor{b l a c k}{20}}} \frac{n}{\cancel{\textcolor{red}{20}}} = 2$

$n = 2$