On a new year eve, every student of a class sends a card to every other student. If the total number of cards delivered is 1980, how many students are there in the class ?

A basket contains eight white and ten black balls. Two draws of one ball each are made without replacement. What is the probability that one ball is white and the other ball is black ?

Two balls can be drawn from 18 balls in ^{18}C_{2} Ways, ie 153 ways. One white from 8 white balls can be drawn in ^{8}C_{1} = 8 ways and one black ball from 10 black can be drawn in ^{10}C_{1} = 10 ways.

A tank is completely filled in 16 hours but takes four hours more to fill because of a leak in the bottom of the bank. What time will the leak take to empty the completely filled tank ?

A person 'X' can do a piece of work in 75 days and 'Y' can do the same piece of work in 45 days. They work together for 15 days and then 'X' leaves. In how many days will' Y' finish the work ?

Direction (Q. 6-10): Following pie-chart shows the percentage distribution of total students who appeared in board exam from different schools. The table shows the ratio of the number of boys to that of girls and the ratio of passed to failed students.

Total number of students who appeared in exam = 48000

School

Boys : Girls

Pass : Fail

A

5 : 3

2 : 1

B

9 : 7

1 : 1

C

2 : 3

3 : 2

D

6 : 7

8 : 5

E

3 : 1

2 : 1

F

8 : 7

3 : 2

What is the total number of boys who appeared in board exam from all six schools together ?