Three-sevenths of a number 21. Find the number

Question

How would I go about writing out/solving the "Three-sevenths of a number" part? I'm confused

Answer 1

You are saying that 3/7 of a number = 21. (let the variable x be "a number"). This can be written as (3/7)x = 21.

 

Now you just need to divide each side by 3/7 to find what x is.

 

x = 21/(3/7)

x = 49

Answer 2

(3/7)21 = 9   In math the word "of" represents multiplication. To multiply, you first divide 21 by 7 to get 3; then multiply 3 by 3 to get 9.