Question

A bag has red and white counters in the ratio 4:7. If I add 4 white counters the ratio becomes 1:2. Work out the number of red counters in the bag.

Answer 1

`(4x)/(7x+4)=(1)/(2)\\ 7x+4=8x\\ x=4\\\\ 4x=4\cdot4=16`
16 red marbles