Mary's sister is 7 years older than Mary. Their combined ages add up to 35. How old is mary?

Question

Solve each problem by writing and solving an equation.

Answer 1

let s is Marys sister age and m is Marys age. According the presentation we have.

s = m + 7 (1)  and  s + m = 35 (2).  from the (2) we get  m = 35 - s plugging this value of m to (1) we get

s = 35-s+7  --->>>  2s=42  so  s=42/2 = 21  and from m=35-s we get m=35-21  so  m = 14

so marys age is 14 years and marys sister age is 21 years