If a brother and a sisters age is 4:3 and if the brother is 12 years old how old will the sister be?
b = brothers age
s = sisters age
A brother and a sisters age is 4:3 means:
b / s = 4 / 3
Brother is 12 years old so:
b / s = 4 / 3
12 / s = 4 / 3
Cross multiply
12 ∙ 3 = s ∙ 4
36 = 4 s
Divide both sides by 4
9 = s
s = 9 yrs old