Question

The ratio of the pocket money saved by a boy and his sister is 5:4. If the brother saves Rs 100 more, how much more should the sister save in order to keep the ratio of their savings unchanged ? 

Answer 1

Let money saved by the boy and her sister be Sx and 4x and let the sister need to save Rs y more 

`(5"x" + 100)/(4"x" + "y") = 5/4`

⇒ 20x + 400 = 20x + 5y

⇒ 5y = 400

⇒ y = 80

The sister needs to save Rs 80 more.