The average of nine numbers is 50. The average of first five numbers is 54 and that of the last three numbers is 52, then the sixth number is -

A can do a piece of work in 4 hours; B and C can do it in 3 hours; A and C can do it in 2 hours. How long will B along take to do it?

A cricketer's average score in 10 innings was 36. In his 11th innings, he scored some runs because of which his average increased to 40. What was his score in 11th innings?

If two numbers are respectively 20% and 50% of a third number, what is the percentage of the first number to the second?

In a school $${1\over10} $$ of the boys are same in number as $${1\over4}$$ of the girls and  $${5\over8} $$ of the girls are same in number as $${1\over4}$$   of the boys. The ratio of the boys to girls in that school is: 

9 persons are seated around a round table. What is the probability that two particular persons sit together?

The compound interest on 12000 for 9 months at 20 % per annum , interest being compounded quarterly is 

A student has to score 33% marks to pass. He gets 117 marks and fails by 81 marks. Find the student’s marks percentage?