Question

At present Disha’s mother is three times the age of Disha. After 5 years their ages will sum up to 70 years. Find the present age.

(a) Disha 10 and her mother 30

(b) Disha 12 and her mother 36

(c) Disha 13 and her mother 39

(d) Disha 15 and her mother 45

This question was posed to me during an interview.

This interesting question is from Solving Linear Equations with Variables on Both the Sides topic in division Linear Equations in One Variable of Mathematics – Class 8

Answer 1

Right answer is (d) Disha 15 and her mother 45

Best explanation: Let Disha’s age be x years then her mother would be 3x years old. After 5 years, their ages are x + 5 (Disha) and 3x + 5 (Disha’s Mother) respectively.

(x + 5) + (3x + 5) = 70

∴ x + 5 + 3x + 5 = 70

∴ 4x + 10 = 70

∴ 4x = 60

∴ x = 15

Since x = 15 we know that Disha’s present age is 15 years, to find her mother’s age we have (3×15) i.e. 45 years.