Q1. There are 12 intermediate stations between two places A and B. In how many ways can a train made to stop at 4 of these 12 intermediate stations that no two stations are consecutive? Directions for Q2 to Q5 A regular six-faced dice has 21 spots altogether. Without looking at any dice you might have lying around, answer these questions : Q2. How many of these spots are in the center of the face on which they are present? Q3. How many of these spots are at one corner or another? Q4. How many spots are neither at the center not at corners Q5. How many pairs of opposite faces are there such that both have a dot in their center? Q6. The number of ways of dividing 20 dissimilar objects into 3 groups of 10, 4 and 6 is Q7. In how many ways can 5 students and 5 teachers sit around a circular table so that no two teachers sit together? |
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Q6. The number of ways of dividing 20 dissimilar objects into 3 groups of 10, 4 and 6 is
a. 10! 4! 6!
b. 10! + 4! + 6!
c. 20!/(10! * 10!)
d. C (20, 10) * C (10, 4)
e. C (20, 10) * C (6, 4)
Sol. 20C10 x 10C4 x 6C6
Q7. In how many ways can 5 students and 5 teachers sit around a circular table so that no two teachers sit together?
a. (4!)^2
b. (5!)^2
c. 4! * 5!
d. 5! * P (6, 5)
Sol. (5-1)! x 5!
4! x 5!
Qus 2 to 5.
2. b
3. b
4. d
5. d
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