राम, हरि की तुलना में तीन गुना कुशल कामगार है। वे दोनों मिलकर एक कार्य को 21 दिनों में पूरा कर सकते हैं। राम अकेला उस कार्य को कितने दिनों में पूरा करेगा?

If P and Q together can complete a piece of work in 15 days and P alone can do it in 45 days, in how many days can Q alone complete that work?

A can lay a railway track between two stations in 16 days and B can do the same job in 12 days. With the help of C, they finished the job in 4 days. In how many days can C alone do the job?