Quantitative Aptitude - Arithmetic Ability Questions

Present age of A is 2 times the present age of B. After 8 years the B's age will be 4 times of C's present age. If C celebrated his fifth birthday 9 years
ago, then what is the present age (in years) of A?

The average of 21 numbers is 12. The average of the first 11 numbers is 9 and the average of the last 11 numbers is 15. What is the value of the middle number?

What is the average of all numbers between 8 and 74 which are divisible by 7?

P and Q can do a project in 20 and 12 days respectively. In how many days can they complete 40% of the project if they work together?

If two marbles are picked at random, what is the probability that either both are red or both are green?

In an examination, 52% candidates failed in English and 42% failed in Mathematics. If 17% failed in both the subjects, then what percent passed in both the subjects?

In an acute-angled triangle ABC is Sin(B+A+C)=32 and tan(C+A-B)=1, then C is equal to

What is the area (in sq cm) of an equilateral triangle of side 6 cm?