How many images of himself can an observer see in a room whose ceiling and two adjacent walls are mirrors?

In how many ways can 5 girls and 3 boys be seated in a row so that no two boys are together ?

In how many ways can 5 girls and 3 boys be seated in a row so that no two boys are together?

In how many ways three girls and nine boys can be seated in two vans, each having numbered seats, 3 in the front and 4 at the back? How many seating arrangements are possible if 3 girls sit together in a back row on adjacent seats?Now, if all the seating arrangements are equally likely, what is the probability of 3 girls sitting together in a back row on adjacent seats?

How many five-digit numbers can be made having exactly two identical digits?

In how many different ways 4 boys and 3 girls can be sitted in one row so that two girls are not together?

How many maximum number of common tangents of two circles can be drawn intersecting at two different points ?

How many ways the three angular points of a regular decagon can be selected so that no two angular points are consecutive.

In how many ways can six students be seated in a line so that two particular students do not sit together?

In how many different ways ten 10 paise and five 5- paise coins can be arranged in a row so that two 5- paise coins are not together ?