How many times the keys of a typewriter have to be pressed in order to write number from 121 to 1346?

The average of some natural numbers is 15. If 30 is added to first number and 5 is subtracted from the last number, the average become 17.5. then the numbers of natural numbers is :

A drink of chocolate and milk contains 8% pure chocolate by volume. If 10 litres of pure milk are added to 50 litres of this drink, the percentage of chocolate in the new drink is:

Two pipes, D and E, can fill a cistern in 26 and 78 hours, respectively, while working alone. If the two pipes are opened together, the time taken to fill the cistern is:

Some litres of acid were drawn off a 54-litre vessel full of acid and an equal amount of water added. Again, the same volume of the mixture was drawn off and replaced by water. As a result, the vessel contained 24 litre of pure acid. How much of the acid was drawn off initially?

A train is 125 m long. If the train takes 30 seconds to cross a tree by the railway line, then the speed of the train is:

The centroid of a ∆ABC is G. The area of ∆ABC is 60 cm². The area of ∆GBC is

A goat is tied with a 10.5 m-long rope to one corner of a plot which is in the shape of an equilateral triangle each side of which is 16 m long. Find the area that the goat can graze on.