If a²=b+c, b²=c+a  and c²=a+b then the  value of $$ {1\over{1+a}}+{1\over{1+b}}+{1\over{1+c}}$$ is

Two numbers are respectively 10% and 25% more than a third number. What percent is the first of the second number?

A goods train 350 m long passes through a tunnel of length 1250 m in 80 seconds. What is the speed of the train?

Find the standard deviation of the following data (rounded off to two decimal places). 

5, 3, 4, 7 

For what value of m will the system of equations 18x-72y+13=0 and 7x-my-17=0 have no solution?

The average of all the numbers between 6 and 50 which are divisible by 5 is

If the compound interest on a certain sum for two consecutive years is Rs.220 and Rs.242, then the rate of interest per annum is 

The smallest number which when divided by 18, 24, 38 and 42 leaves the remainder 15, 21,     35 and 39 respectively is :-