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

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Answer 1 · 2017-01-13T14:57:35

See full explanation for finding the number below

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 $n$ $n$ .

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

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

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

$20 n - 15$ $20n - 15$

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

$20 n - 15 = 25$ $20n - 15 = 25$

We can now solve:

$20 n - 15 + 15 = 25 + 15$ $20n - 15 + color(red)(15) = 25 + color(red)(15)$

$20 n - 0 = 40$ $20n - 0 = 40$

$20 n = 40$ $20n = 40$

$20 \frac{n}{20} = \frac{40}{20}$ $20n/color(red)(20) = 40/color(red)(20)$

$color(red)(cancel(color(black)(20)))n/cancel(color(red)(20)) = 2$

$n = 2$