Answer<\/span><\/summary>\nAnswer: (b) -1
\nFirst we find 10
\nSo, 10 = 1
\nNow, -10 = -1<\/p>\n<\/details>\n
\nQuestion 3.
\nIf the fourth term in the expansion (ax + 1\/x)\u207f is 5\/2, then the value of x is
\n(a) 4
\n(b) 6
\n(c) 8
\n(d) 5<\/p>\n\nAnswer<\/span><\/summary>\nAnswer: (b) 6
\nGiven, T4<\/sub> = 5\/2
\n\u21d2 T3+1<\/sub> = 5\/2
\n\u21d2 \u207fC3<\/sub> \u00d7 (ax)n-3<\/sup> \u00d7 (1\/x)\u00b3 = 5\/2
\n\u21d2 \u207fC3<\/sub> \u00d7 an-3<\/sup> \u00d7 xn-3<\/sup> \u00d7 (1\/x)\u00b2 = 5\/2
\nClearly, RHS is independent of x,
\nSo, n – 6 = 0
\n\u21d2 n = 6<\/p>\n<\/details>\n
\nQuestion 4.
\nThe number 111111 \u2026\u2026\u2026\u2026.. 1 (91 times) is
\n(a) not an odd number
\n(b) none of these
\n(c) not a prime
\n(d) an even number<\/p>\n\nAnswer<\/span><\/summary>\nAnswer: (c) not a prime
\n111111 \u2026\u2026\u2026\u2026.. 1 (91 times) = 91 \u00d7 1 = 91, which is divisible by 7 and 13.
\nSo, it is not a prime number.<\/p>\n<\/details>\n
\nQuestion 5.
\nIn the expansion of (a + b)\u207f, if n is even then the middle term is
\n(a) (n\/2 + 1)th<\/sup> term
\n(b) (n\/2)th<\/sup> term
\n(c) nth<\/sup> term
\n(d) (n\/2 – 1)th<\/sup> term<\/p>\n\nAnswer<\/span><\/summary>\nAnswer: (a) (n\/2 + 1)th<\/sup> term
\nIn the expansion of (a + b)\u207f
\nif n is even then the middle term is (n\/2 + 1)th<\/sup> term<\/p>\n<\/details>\n
\nQuestion 6.
\nThe number of terms in the expansion (2x + 3y – 4z)\u207f is
\n(a) n + 1
\n(b) n + 3
\n(c) {(n + 1) \u00d7 (n + 2)}\/2
\n(d) None of these<\/p>\n\nAnswer<\/span><\/summary>\nAnswer: (c) {(n + 1) \u00d7 (n + 2)}\/2
\nTotal number of terms in (2x + 3y – 4z)\u207f is
\n= n+3-1<\/sup>C3-1<\/sub>
\n= n+2<\/sup>C2<\/sub>
\n= {(n + 1) \u00d7 (n + 2)}\/2<\/p>\n<\/details>\n
\nQuestion 7.
\nIf A and B are the coefficient of x\u207f in the expansion (1 + x)2n<\/sup> and (1 + x)2n-1<\/sup> respectively, then A\/B equals
\n(a) 1
\n(b) 2
\n(c) 1\/2
\n(d) 1\/n<\/p>\n\nAnswer<\/span><\/summary>\nAnswer: (b) 2
\nA\/B = \u00b2\u207fCn<\/sub>\/ 2n-1<\/sup>Cn<\/sub>
\n= {(2n)!\/(n! \u00d7 n!)}\/{(2n – 1)!\/(n! \u00d7 (n – 1!))}
\n= {2n(2n – 1)!\/(n(n – 1)! \u00d7 n!)}\/{(2n – 1)!\/(n! \u00d7 (n – 1!))}
\n= 2
\nSo, A\/B = 2<\/p>\n<\/details>\n
\nQuestion 8.
\nThe coefficient of y in the expansion of (y\u00b2 + c\/y)5<\/sup> is
\n(a) 29c
\n(b) 10c
\n(c) 10c\u00b3
\n(d) 20c\u00b2<\/p>\n\nAnswer<\/span><\/summary>\nAnswer: (c) 10c\u00b3
\nWe have,
\nTr+1<\/sub> = 5<\/sup>Cr<\/sub> \u00d7(y\u00b2)5-r<\/sup> \u00d7 (c\/y)r<\/sup>
\n\u21d2 Tr+1<\/sub> = 5<\/sup>Cr<\/sub> \u00d7 y10-3r<\/sup> \u00d7 cr<\/sup>
\nFor finding the coefficient of y,
\n\u21d2 10 – 3r = 1
\n\u21d2 33r = 9
\n\u21d2 r = 3
\nSo, the coefficient of y = 5<\/sup>C3<\/sub> \u00d7 c\u00b3
\n= 10c\u00b3<\/p>\n<\/details>\n
\nQuestion 9.
\nThe coefficient of x-4<\/sup> in (3\/2 – 3\/x\u00b2)10<\/sup> is
\n(a) 405\/226
\n(b) 504\/289
\n(c) 450\/263
\n(d) None of these<\/p>\n\nAnswer<\/span><\/summary>\nAnswer: (d) None of these
\nLet x-4<\/sup> occurs in (r + 1)th term.
\nNow, Tr+1<\/sub> = 10<\/sup>Cr<\/sub> \u00d7 (3\/2)10-r<\/sup> \u00d7(-3\/x\u00b2)r<\/sup>
\n\u21d2 Tr+1<\/sub> = 10<\/sup>Cr<\/sub> \u00d7 (3\/2)10-r<\/sup> \u00d7(-3)r<\/sup> \u00d7 (x)-2r<\/sup>
\nNow, we have to find the coefficient of x-4<\/sup>
\nSo, -2r = -4
\n\u21d2 r = 2
\nNow, the coefficient of x-4<\/sup> = 10<\/sup>C2<\/sub> \u00d7 (3\/2)10-2<\/sup> \u00d7 (-3)2<\/sup>
\n= 10<\/sup>C2<\/sub> \u00d7 (3\/2)8<\/sup> \u00d7 (-3)2<\/sup>
\n= 45 \u00d7 (3\/2)8<\/sup> \u00d7 9
\n= (312<\/sup> \u00d7 5)\/28<\/sup><\/p>\n<\/details>\n
\nQuestion 10.
\nIf n is a positive integer, then 9n+1<\/sup> – 8n – 9 is divisible by
\n(a) 8
\n(b) 16
\n(c) 32
\n(d) 64<\/p>\n\nAnswer<\/span><\/summary>\nAnswer: (d) 64
\nLet n = 1, then
\n9n+1<\/sup> – 8n – 9 = 91+1<\/sup> – 8 \u00d7 1 – 9 = 9\u00b2 – 8 – 9 = 81 – 17 = 64
\nwhich is divisible by 64
\nLet n = 2, then
\n9n+1<\/sup> – 8n – 9 = 92+1<\/sup> – 8 \u00d7 2 – 9 = 9\u00b3 – 16 – 9 = 729 – 25 = 704 = 11 \u00d7 64
\nwhich is divisible by 64
\nSo, for any value of n, 9n+1<\/sup> – 8n – 9 is divisible by 64<\/p>\n<\/details>\n
\nQuestion 11.
\nThe general term of the expansion (a + b)\u207f is
\n(a) Tr+1<\/sub> = \u207fCr<\/sub> \u00d7 ar<\/sup> \u00d7 br<\/sup>
\n(b) Tr+1<\/sub> = \u207fCr<\/sub> \u00d7 ar<\/sup> \u00d7 bn-r<\/sup>
\n(c) Tr+1<\/sub> = \u207fCr<\/sub> \u00d7 an-r<\/sup>\u00d7 bn-r<\/sup>
\n(d) Tr+1<\/sub> = \u207fCr<\/sub> \u00d7 an-r<\/sup> \u00d7 br<\/sup><\/p>\n\nAnswer<\/span><\/summary>\nAnswer: (d) Tr+1<\/sub> = \u207fCr<\/sub> \u00d7 an-r<\/sup> \u00d7 br<\/sup>
\nThe general term of the expansion (a + b)\u207f is
\nTr+1<\/sub> = \u207fCr<\/sub> \u00d7 an-r<\/sup> \u00d7 br<\/sup><\/p>\n<\/details>\n
\nQuestion 12.
\nIn the expansion of (a + b)\u207f, if n is even then the middle term is
\n(a) (n\/2 + 1)th<\/sup>\u00a0term
\n(b) (n\/2)th<\/sup> term
\n(c) nth<\/sup> term
\n(d) (n\/2 – 1)th<\/sup> term<\/p>\n\nAnswer<\/span><\/summary>\nAnswer: (a) (n\/2 + 1)th<\/sup>\u00a0term
\nIn the expansion of (a + b)\u207f,
\nif n is even then the middle term is (n\/2 + 1)th<\/sup> term<\/p>\n<\/details>\n
\nQuestion 13.
\nThe smallest positive integer for which the statement 3n+1<\/sup> < 4\u207f is true for all
\n(a) 4
\n(b) 3
\n(c) 1
\n(d) 2<\/p>\n\nAnswer<\/span><\/summary>\nAnswer: (a) 4
\nGiven statement is: 3n+1<\/sup> < 4\u207f is
\nLet n = 1, then
\n31+1<\/sup> < 41<\/sup> = 3\u00b2 < 4 = 9 < 4 is false
\nLet n = 2, then
\n32+1<\/sup> < 4\u00b2 = 3\u00b3 < 4\u00b2 = 27 < 16 is false
\nLet n = 3, then
\n33+1<\/sup> < 4\u00b3 = 34<\/sup> < 4\u00b3 = 81 < 64 is false
\nLet n = 4, then
\n34+1<\/sup> < 44<\/sup> = 35<\/sup> < 44<\/sup> = 243 < 256 is true.
\nSo, the smallest positive number is 4<\/p>\n<\/details>\n
\nQuestion 14.
\nThe number of ordered triplets of positive integers which are solution of the equation x + y + z = 100 is
\n(a) 4815
\n(b) 4851
\n(c) 8451
\n(d) 8415<\/p>\n\nAnswer<\/span><\/summary>\nAnswer: (b) 4851
\nGiven, x + y + z = 100
\nwhere x \u2265 1, y \u2265 1, z \u2265 1
\nLet u = x – 1, v = y – 1, w = z – 1
\nwhere u \u2265 0, v \u2265 0, w \u2265 0
\nNow, equation becomes
\nu + v + w = 97
\nSo, the total number of solution = 97+3-1<\/sup>C3-1<\/sub>
\n= 99<\/sup>C2<\/sub>
\n= (99 \u00d7 98)\/2
\n= 4851<\/p>\n<\/details>\n
\nQuestion 15.
\nif n is a positive ineger then 2\u00b3\u207f – 7n – 1 is divisible by
\n(a) 7
\n(b) 9
\n(c) 49
\n(d) 81<\/p>\n\nAnswer<\/span><\/summary>\nAnswer: (c) 49
\nGiven, 2\u00b3\u207f – 7n – 1 = 23\u00d7n<\/sup> – 7n – 1
\n= 8\u207f – 7n – 1
\n= (1 + 7)\u207f – 7n – 1
\n= {\u207fC0<\/sub> + \u207fC1<\/sub> 7 + \u207fC2<\/sub> 7\u00b2 + …….. + \u207fCn<\/sub> 7\u207f} – 7n – 1
\n= {1 + 7n + \u207fC2<\/sub> 7\u00b2 + …….. + \u207fCn<\/sub> 7\u207f} – 7n – 1
\n= \u207fC2<\/sub> 7\u00b2 + …….. + \u207fCn<\/sub> 7\u207f
\n= 49(\u207fC2<\/sub> + …….. + \u207fCn<\/sub> 7n-2<\/sup>)
\nwhich is divisible by 49
\nSo, 2\u00b3\u207f – 7n – 1 is divisible by 49<\/p>\n<\/details>\n
\nQuestion 16.
\nThe greatest coefficient in the expansion of (1 + x)10<\/sup> is
\n(a) 10!\/(5!)
\n(b) 10!\/(5!)\u00b2
\n(c) 10!\/(5! \u00d7 4!)\u00b2
\n(d) 10!\/(5! \u00d7 4!)<\/p>\n\nAnswer<\/span><\/summary>\nAnswer: (b) 10!\/(5!)\u00b2
\nThe coefficient of xr in the expansion of (1 + x)10<\/sup> is 10<\/sup>Cr<\/sub> and 10<\/sup>Cr<\/sub> is maximum for r = 10\/ = 5
\nHence, the greatest coefficient = 10<\/sup>C