11.Formula for the calculation of co-efficient of variation is

12.If the radius of a circle is decreased by 50%,then its area is reduced by

13.The population of a town is 18,000.It increased by 10% during the first year and by 20% during the second year.The population after 2 years will be

14.Ten years ago A was half of B in age .If the ratio of their present ages is 3:4,what will be the total of their present ages?

15.If the average of first six numbers is 58 and that of the last six is 63,the value of the sixth number is #Q The average of 11 numbers is 60.If the average of first six numbers is 58 and that of the last six is 63,the value of the sixth number is