Cpt quantitative aptitude problem

please tell me the correct answers and explain it too how you get those figures...thanx in advance :)

The ratio compounded of 4:9, the duplicate ratio of 3:4, the triplicate ratio of 2:3 and 9:7 is

1. 2:7
2. 7:2
3. 2:27
4. None of these

P, Q and R are three cities. The ratio of average temperature between P and Q is 11:12 and that between P and R is 9:8. The ratio between the average temperature of Q and R is

1. 22:27
2. 27:22
3. 32:33
4. None of these

If 2s:3t is the duplicate ratio of 2s-p: 3t-p then

1. P2(P2 is square of P) = 6st
2. P = 6st
3. 2P = 3st
4. None of these