A takes 9 days more than B to do a certain piece of work. Together they can do the work in 6 days. How many days will A alone take to do the work ?

A man bought a certain number of chairs for ₹ 10000. He kept one for his own use and sold the rest at the rate ₹ 50 more than he gave for one chair. Besides getting his own chair for nothing, he made a profit of ₹ 450. How many chairs did he buy ?

If a : b = 2 : 3, b : c = 4 : 5 and c : d = 6 : 7, find a : b : c : d.