Quantitative Aptitude - Arithmetic Ability Questions

If the mean of m observations out of n observations is n and the mean of remaining observations is m, then what is the mean of all n observations?

In a computer game, there are builders and destroyers. Together there are 20 of them. Some of them try to build a wall around a castle while the rest try to demolish it. Each of the builders can build the wall alone in 15 hours while any of the destroyers can demolish it in 10 hours. If all 20 builders and destroyers are made active when there is no wall and the wall gets built in 3 hours, how many of them are destroyers?

A & B together finish a job in 24 days, while A, B & C together can finish the same job in 8 days. C alone will finish the job in

The average age of Hari, his wife and their two children is 23 years. His wife is just 4 years younger than Hari and his wife was 20 years old when their daughter was born. He was 28 years old when their son was born. What is the sum of the age of Hari and his daughter is?

P and Q invested some money in a business in the ratio of 4 : 7 respectively. After 6 months P withdraws his capital. If they receive profits in the ratio of 4 :21, then for how many months did Q invest in the business?

A bus starts running with the initial speed of 21 km/hr and its speed increases every hour by 3 km/hr. How many hours will it take to cover a distance of 252 km?

Priya’s age was cube of an integral number (different from 1) four years ago and square of an integral number after four years. How long should she wait so that her age becomes square of a number in the previous year and cube of a number in the next year?

If 1 shirt is offered free on purchase of 4 shirts, what is the effective discount (in %) on each shirt?