Question

Please help solve for n. 5/15 = n/21 a. n = 35 b. n = 7 c. n = 5 d. n = 90

Answer 1

b. n = 7

Explanation:

You want to solve the proportion ...

5/15 = n/21

This is most easily done by multiplying by the inverse of the coefficient of the variable:

(21/1)(5/15) = (21/1)(n/21)

7 = n . . . . . . . . . simplify

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Additional comment

The math is a little easier if you simplify 5/15 to 1/3. Then, n = 21/3 = 7.