Calculate the standard deviation of the following data: 7, 8, 9, 10, 11, 12, 13 

A number is selected at random between 20 and 30, both numbers inclusive. Find the probability that the number is a prime. 

The equation of the line in the graph is 

Express the product of 0.0014 and 0.011 in standard form 

A school boy lying on the ground 30m away from the foot of a water tank towel observes that the angle of elevation of the top of the tank is 60\(^o\). Calculate the height of the tank.