Question Bank No: 1

1. For each n N,23n1is divisible by

 a)8
 b)16
 c)32
 d)none of these

2. x (xn1nan1)+an(n1)is divisible by (xa)2 for

 a)n>1
 b)n>2
 c)all n N
 d)none of these

323n7n1is divisible by

 a)64
 b)36
 c)49
 d)25

4. If n is a positive integer, then n3+2nis divisible by

 a)3
 b)2
 c)6
 d)5

5. If m, n are any two odd positive integer with n < m, then the largest positive integers which divides all the numbers of the type m2 n2 is

 a)4
 b)6
 c)8
 d)9

6. The smallest positive integer for which the statement 3n+1< 4n holds is

 a)1
 b)2
 c)3
 d)4

7. P(n) : 2n+2 < 3n, is true for

 a)all
 b)for n > 3
 c)all n > 2
 d)None of these

8. If P(n) : 3n > 4n, then P(n) is true for

 a)n = 2
 b)n > 2
 c)n > 1
 d)None of these

9. The inequality n!>2n1 is true

 a)for all n > 1
 b)for all n > 2
 c)for all
 d)for no

10. P(n):32n+28n9 is divisible by 64, is true for

 a)all n N{0}
 b)n2,nN
 c)n2,n>N
 d)none of these

11. The statement P(n):1×1!+2×2!+3×3!+....+n×n!=(n+1)!1 is

 a)true of all n >1
 b)true for no n
 c)true for all n N
 d)None of these

12. A student was asked to prove a statement by induction. He proved (i) P(5) is true and (ii) truth of P(n) truth of P(n+), n N. On the basis of this, he could conclude that P(n) is true

 a)for no n
 b)for all n5
 c)for all n
 d)None of these

13. The greatest positive integer which divides (n+1)(n+2)(n+3)......(n+r)for nNis

 a)r
 b)r!
 c)n+r
 d)(r+1)!

14. Let P(n): n2+nis an odd integer. It is seen that truth of P(n) the truth of P(n+1). Therefore P(n) is true for all

 a)n>1
 b)n
 c)n>2
 d)none of these

15. The greatest positive integer, which divides (n+16)(n+17)(n+18)(n+19), for all n N,is

 a)2
 b)4
 c)24
 d)120

16. If P(x): 2+4+6+....+2n, nN,then P(m) =m(m+1)+2
P ( m + 1 ) = ( m + 1 ) ( m + 3 ) + 2 m N . So we can conclude that P(n) = n(n+1)+2 for

 a)n>1
 b)n>2
 c)all nN
 d)nothing can be said

17. The smallest +ve integer n for which n!<(n+12)nholds is

 a)1
 b)2
 c)3
 d)4

18. If X >1,then the statement P(n): (1+x)n>1+ nx is true for

 a)all n N
 b)all n >1
 c)all n >1andx0
 d)None of these

19. If P(n): 2n <n!,nN,then P(n) is true for

 a)all n
 b)all n >2
 c)all n >3
 d)None of these

20. If P(n) is a statement such that truth of P(n) the truth of P(n+1) for n N,then P(n) is true

 a)for all n
 b)for all n >1
 c)for all n>m,m is some fixed positive integer
 d)nothing can be said