At what simple rate of interest a sum is double in 8 years?

$$ {a^2-b^2-2bc-c^2}\over{a^2+b^2+2ab-c^2}$$ is equal to

The least multiple of 7, which leaves the remainder 4, when divided by any of 6, 9, 15 and 18, is 

ΔABC is similar to ΔDEF. Length of AB is 18 cm and  length of the corresponding side  DE is 10 cm. What is the ratio  of Perimeter of ΔABC : Perimeter of ΔDEF?

Two pipes A and B can fill a tank in 3 hours and 5 hours. Then, if all three are open, the tank is filled in 30 hours. Find in how many hours a third pipe will empty the tank?

P and Q can do a piece of work in 12 days, Q and R can do a piece of work in 15 days and R and P can do a piece of work in 20 days. Q alone can do the whole work in

The edges of a cuboid are in the ratio 1 : 2: 3 and its surface area is  88 sq.cm. The volume of the cuboid is:

In two types of brass ratio of copper and zinc are 8: 3 and 15: 7 respectively. The ratio in which these two types of brass should be mixed, so that the ratio of copper and zinc in this new type of brass become 5: 2 is