Ratio GCSE Word Problem

Question

In a box, the ratio of the number of balls to the number of marbles is 3:7. If 75 more balls were added and 75 marbles were removed, the ratio will be 4:1. How many balls were there at first ?

 

 

I realised that 3x+75 = balls and 7x-75 = marbles but I don't know what to do.

 

Thank You

Answer 1

You are correct as far as you go.

3x + 75 : 7x - 75 :: 4 : 1        new proportion

3x + 75 = 4(7x - 75)              product means/extremes

 

Can you solve for x and answer?