Let x = "my" age. Then the sister's age = x+15. The sum of ages equation is x + (x+15) = 49. 2x + 15 = 49 2x = 49 - 15 = 34. x = 34/2 = 17. ANSWER. My age is 17. The sister's age is 17+15 = 32. CHECK. 17 + 32 = 49. ! Correct !