Question

Lauren brings brownies to class one day. She gives 3/5 of them to her friends Gareth, Tammy, and Camilla. If she gave them 21 brownies, how many did she bring to class?

Answer 1

If 3/5 of all the brownies is 21, then 5/3 of 21 is the number of the brownies that Lauren brought in.

That probably sounded super confusing. When multiplying a number by a reciprocal of a fraction (a fraction where the numerator and denominator is reversed), the previous fraction multiplication is reversed.

Multiplying 21 with 5/3 will give us the original number of brownies.

$21 \times \dfrac{5}{3}=35$

Lauren originally brought 35 brownies.

Answer 2

3/5=21
5/5= 21/3 x 5
35 brownies