Permutation, Combination and Probability Page-3
17) Which of the following sets in infinite?
(A) the set of student of your class
(B) the set of all schools in the USA
(C) the set of natural numbers between 3 and 10
(D) the set of rational numbers between 3 and 10

View Answer

Answer: Option D

Solution:
The number of rational numbers between 3 and 10 is infinite
18) i-3 = ___
(A) i
(B) 1
(C) -1
(D) -i

View Answer

Answer: Option A

Solution:
i -3 =
1/i3
=
1/i2 i
= -
1/i
=
i2/i
= i

19) If nP2 = 30 then n = ?
(A) 32
(B) 6
(C) 5
(D) 28

View Answer

Answer: Option B

Solution:
6.5.4 =
n!/(n-2)!

= 30
n(n-1) (n-2)!/(n-2)!
= 30
n(n-1) = 6.5
n = 6

20) If nC8 = nC12 then n = ?
(A) 20
(B) 4
(C) 96
(D) none of these

View Answer

Answer: Option A

Solution:
nC8 = nC12 = nCn-12
8 = n-12
n = 20