Question

Translate the following sentence into an equation using n for the unknown number. Then solve for n.

when 15 is decreased by three times a number, the result is 21
a.
15 - 372 = 21
n = -2
b.
312 - 15 = 21
n = -2
C.
31 - 15 = 21
n = 12
d.
15 - 3n2 = 21
n-2

Answer 1

a

Explanation:

Answer 2

Given:

15 is decreased by three times a number, the result is 21.

To find:

The equation for the given statement and solve it.

Solution:

Let n be the unknown number. Then,

Three times of a number =
`3n`

15 is decreased by three times a number =
`15-3n`

It is given given that the result after subtraction is 21. So,

`15-3n=21`

`-3n=21-15`

`-3n=6`

Divide both sides by -3.

`n=(6)/(-3)`

`n=-2`

Therefore, the required equation is
`15-3n=21` and its solution is
`n=-2`. Hence, the correct option is (a).