Find the sum of all prime numbers between 10 and 90.

A certain sum of money lent out at simple interest amounts to Rs. 2400 in 4 years and Rs. 3000 in 6 years. Find the rate of interest per annum?

Sanjay invested Rs. 48000 in two different parts one at 10% CI (Compounded half yearly) and another one at 15% SI. At the end of the year he received total interest Rs. 5490, then find the amount invested in SI?

The expenses on rice, fish and oil of a family are in the ratio 12 : 17 : 3. The price of these articles are increased by 20 % , 30 % and 50 % respectively. The total expenses of family on these articles are increased by: 

α and β  is two root of a equations $$2x^2-7x+ 12=0 $$ then the value of $$ {α \over β }  + {β \over α }=? $$

A boat is moving away from an observation tower. It makes an angle of depression of 60 ° with an observer's eye when at a distance of 50 m from the tower. After 8 sec, the angle of depression becomes 30 °. By assuming that it is running in still water, the approximate speed of the boat is 

An alloy contains copper and tin in the ratio 3: 2. If 250 gm of copper is added to this alloy then copper in it becomes double the quantity of tin in it. What is the amount (in gm) of tin in the alloy?