Question

my son is x year old ,in five years time i will be twice his age and both our ages will be multiples of 10.the sum of ages will be between 50 and 100.how old am i

Answer 1

son's age : (x+5) in 5 years.
Parent's age: 2(x+5) in 5 years.

50 < ((x+5) + 2(x+5))< 100,
50 < (x+5 + 2x+10) < 100,
50 < 3x+15 < 100,
50-15 < 3x < 100-15,
35 < 3x < 85,
35/3 < x < 85/3.
11 2/3 < X < 28 1/3,
16 2/3 < x+5 < 33 1/3,

(x+5) = 20 years = The son's age.

2(x+5) = 40 years = The parent's age.

Answer 2

55