Question

John is twice as old as Mary. The sum of thelr ages is 21. How old Is Mary?

Answer 1

Answer: 7 years

Explanation:

let x be the age of Mary

so John's age will be 2x

the equation becomes

2x+x=21

3x=21

x=21/3

x=7

Answer 2

Explanation:

Let Mary's age = x years

John's age = 2 * x = 2x

The sum of their ages = 21

x + 2x = 21

3x = 21

Divide both sides by 3

x = 21/3

x = 7

Mary's age = 7 years