A couple of questions..

1. Four friends P,Q,R,S are working on an assignment together. They contribute to the work in the ratio 1:2:3:4 respectively. They can complete the work individually in 1,2,3,4 days respectively. If they work one after the other , how many days does it take to complete the assignment ?

2. The weights of 3 heaps of gold are in the ratio 5:6:7. By what fractions of themselves must the first two be increased so that the ratio of the weights is changed to 7:6:5 ?

ans : 24/25 , 2/5