Mr Lim put some red pens and blue pens into a box . The ratio of the number of red pens to the number of blue pens was 3: 4 .He
pet another 20 red pens into the box and the ratio of the number of red pens to the number of blue pens became 2:1 (a) How many red pens were there in the end? (b) How many blue pens were there?
