EXPONENTS - Questions & Answers
EXERCISE 2(A)1. Multiple Choice Type :
Choose the correct answer from the options given below.
(i) (1/3)-3 - (1/2)-3 is equal to: (a) 1 (b) 1/27 - 1/8 (c) 19 (d) -19 Answer: (c) 19
(ii) (2/3)3 × (3/2)6 is equal to: (a) 8/27 (b) 27/8 (c) 4/9 (d) 9/4 Answer: (b) 27/8
(iii) 80 + 8-1 + 4-1 is equal to: (a) 8 3/8 (b) 3/8 (c) 1 3/8 (d) 2 2/3 Answer: (c) 1 3/8
(iv) (-5)5 × (-5)-3 is equal to: (a) 1/5 (b) 5 (c) -25 (d) 25 Answer: (d) 25
2. Evaluate :
(i) (3-1 × 9-1) ÷ 3-2 Answer: (1/3 × 1/9) ÷ 1/9 = 1/27 × 9 = 1/3
(ii) (3-1 × 4-1) ÷ 6-1 Answer: (1/3 × 1/4) ÷ 1/6 = 1/12 × 6 = 1/2
(iii) (2-1 + 3-1)3 Answer: (1/2 + 1/3)3 = (5/6)3 = 125/216
(iv) (3-1 ÷ 4-1)2 Answer: (1/3 ÷ 1/4)2 = (4/3)2 = 16/9
(v) (22 + 32) × (1/2)2 Answer: (4 + 9) × 1/4 = 13/4 = 3 1/4
(vi) (52 - 32) × (2/3)-3 Answer: (25 - 9) × (3/2)3 = 16 × 27/8 = 2 × 27 = 54
(vii) [(1/4)-3 - (1/3)-3] ÷ (1/6)-3 Answer: [43 - 33] ÷ 63 = [64 - 27] ÷ 216 = 37/216
(viii) [(-3/4)-2]2 Answer: (-3/4)-4 = (-4/3)4 = 256/81
(ix) {(3/5)-2}-2 Answer: (3/5)4 = 81/625
(x) (5-1 × 3-1) ÷ 6-1 Answer: (1/5 × 1/3) ÷ 1/6 = 1/15 × 6 = 2/5
3. If 1125 = 3m × 5n find m and n.
Answer: 1125 = 9 × 125 = 32 × 53. Therefore, m = 2 and n = 3.
4. Find x, if 9 × 3x = (27)2x-3
Answer: 32 × 3x = (33)2x-3 => 32+x = 36x-9. Equating exponents: 2 + x = 6x - 9 => 5x = 11 => x = 11/5.
EXERCISE 2(B)
1. Multiple Choice Type:
Choose the correct answer from the options given below.
(i) If x = 3m and y = 3m+2, x/y is: (a) 9 (b) 1/9 (c) 6 (d) 9 Answer: (b) 1/9
(ii) (x-2 / 3y-1)-1 is equal to: (a) 3x2/y (b) x2/3y (c) y/3x2 (d) 3y/x2 Answer: (d) 3y/x2
(iii) If (4/5)-3 × (4/5)-5 = (4/5)3x-2, the value of x is: (a) 2 (b) 1/2 (c) -2 (d) -1/2 Answer: (c) -2
(iv) If (m/n)x-1 = (n/m)x-5, the value of x is: (a) 3 (b) -3 (c) 1/3 (d) -1/3 Answer: (a) 3
(v) (1/7)-3 × 7-1 × 1/49 is equal to: (a) -1 (b) 1/7 (c) -7 (d) 1 Answer: (d) 1
2. Compute:
(i) 18 × 30 × 53 × 22 Answer: 1 × 1 × 125 × 4 = 500
(ii) (47)2 × (4-3)4 Answer: 414 × 4-12 = 42 = 16
(iii) (2-9 ÷ 2-11)3 Answer: (2-9 - (-11))3 = (22)3 = 26 = 64
(iv) (2/3)-4 × (27/8)-2 Answer: (3/2)4 × (8/27)2 = 81/16 × 64/729 = (81/729) × (64/16) = 1/9 × 4 = 4/9
(v) (56/28)0 ÷ (2/5)3 × 16/25 Answer: 1 ÷ 8/125 × 16/25 = 125/8 × 16/25 = 5 × 2 = 10
(vi) (12)-2 × 33 Answer: 1/144 × 27 = 27/144 = 3/16
(vii) (-5)4 × (-5)6 ÷ (-5)9 Answer: (-5)10 ÷ (-5)9 = (-5)1 = -5
(viii) (-1/3)4 ÷ (-1/3)8 × (-1/3)5 Answer: (-1/3)4-8+5 = (-1/3)1 = -1/3
(ix) 90 × 4-1 ÷ 2-4 Answer: 1 × 1/4 ÷ 1/16 = 1/4 × 16 = 4
(x) (625)-3/4 Answer: (54)-3/4 = 5-3 = 1/125
(xi) (27/64)-2/3 Answer: (64/27)2/3 = ((4/3)3)2/3 = (4/3)2 = 16/9
(xii) (125)-2/3 ÷ (8)2/3 Answer: (53)-2/3 ÷ (23)2/3 = 5-2 ÷ 22 = 1/25 ÷ 4 = 1/100
(xiii) (1/32)-2/5 Answer: (32)2/5 = (25)2/5 = 22 = 4
(xiv) (243)2/5 ÷ (32)-2/5 Answer: (35)2/5 ÷ (25)-2/5 = 32 ÷ 2-2 = 9 ÷ 1/4 = 36
(xv) (-3)4 - (4√3)0 × (-2)5 ÷ (64)2/3 Answer: 81 - 1 × (-32) ÷ 16 = 81 - (-2) = 83
(xvi) (27)2/3 ÷ (81/16)-1/4 Answer: (33)2/3 ÷ (16/81)1/4 = 32 ÷ 2/3 = 9 × 3/2 = 27/2 = 13.5
3. Simplify:
(i) 84/3 + 253/2 - (1/27)-2/3 Answer: (23)4/3 + (52)3/2 - (27)2/3 = 24 + 53 - (33)2/3 = 16 + 125 - 9 = 132
(ii) [(64)-2]-3 ÷ [ {(-8)2}3 ]2 Answer: 646 ÷ (-8)12 = (26)6 ÷ (23)12 = 236 ÷ 236 = 1
(iii) (2-3 - 2-4)(2-3 + 2-4) Answer: (2-3)2 - (2-4)2 = 2-6 - 2-8 = 1/64 - 1/256 = (4-1)/256 = 3/256
4. Evaluate :
(i) (-5)0 Answer: 1
(ii) 80 + 40 + 20 Answer: 1 + 1 + 1 = 3
(iii) (8 + 4 + 2)0 Answer: 1
(iv) 4x0 Answer: 4(1) = 4
(v) (4x)0 Answer: 1
(vi) [(103)0]5 Answer: [1]5 = 1
(vii) (7x0)2 Answer: (7 × 1)2 = 49
(viii) 90 + 9-1 - 9-2 + 91/2 - 9-1/2
Answer: 1 + 1/9 - 1/81 + 3 - 1/3 = 4 + (9 - 1 - 27)/81 = 4 - 19/81 = 3 62/81
5. Simplify:
(i) a5b2 / a2b-3
Answer: a5-2b2-(-3) = a3b5
(ii) 15y8 ÷ 3y3
Answer: 5y8-3 = 5y5
(iii) x10y6 ÷ x3y-2
Answer: x7y8
(iv) 5z16 ÷ 15z-11
Answer: 1/3 z16-(-11) = 1/3 z27
(v) (36x2)1/2
Answer: 6x
(vi) (125x-3)1/3
Answer: 5x-1 = 5/x
(vii) (2x2y-3)-2
Answer: 2-2x-4y6 = y6 / 4x4
(viii) (27x-3y6)2/3
Answer: (33)2/3x-2y4 = 9y4 / x2
(ix) (-2x2/3y-3/2)6
Answer: (-2)6x(2/3)*6y(-3/2)*6 = 64x4y-9 = 64x4 / y9
6. Simplify: (xa+b)a-b . (xb+c)b-c . (xc+a)c-a
Answer: xa2-b2 . xb2-c2 . xc2-a2 = xa2-b2+b2-c2+c2-a2 = x0 = 1
7. Simplify:
(i) 5√x20y-10z5 ÷ x3/y3
Answer: (x4y-2z1) ÷ (x3/y3) = x4-3y-2+3z = xyz
(ii) (256a16 / 81b4)-3/4
Answer: (81b4 / 256a16)3/4 = ((3b / 4a4)4)3/4 = (3b / 4a4)3 = 27b3 / 64a12
8. Simplify and express as positive indices:
(i) (a-2b)-2 . (ab)-3
Answer: a4b-2 . a-3b-3 = a1b-5 = a/b5
(ii) (xny-m)4 × (x3y-2)-n
Answer: x4ny-4m × x-3ny2n = xny2n-4m
(iii) (125a-3 / y6)-1/3
Answer: (y6 / 125a-3)1/3 = y2 / (5a-1) = ay2 / 5
(iv) (32x-5 / 243y-5)-1/5
Answer: (243y-5 / 32x-5)1/5 = 3y-1 / 2x-1 = 3x / 2y
(v) (a-2b)1/2 × (ab-3)1/3
Answer: a-1b1/2 × a1/3b-1 = a-2/3b-1/2 = 1 / (a2/3b1/2)
(vi) (xy)m-n . (yz)n-l . (zx)l-m
Answer: xm-nym-n . yn-lzn-l . zl-mxl-m = x0y0z0 = 1
9. Show that: (xa / x-b)a-b . (xb / x-c)b-c . (xc / x-a)c-a = 1
Answer: (xa+b)a-b . (xb+c)b-c . (xc+a)c-a = xa2-b2 . xb2-c2 . xc2-a2 = x0 = 1
10. Evaluate : x5+n × (x2)3n+1 / x7n-2
Answer: x5+n + 6n+2 - (7n-2) = x7n+7 - 7n+2 = x9
11. Evaluate : a2n+1 × a(2n+1)(2n-1) / [an(4n-1) × (a2)2n+3]
Answer: a2n+1 + 4n2-1 / [a4n2-n + 4n+6] = a4n2+2n / a4n2+3n+6 = a-n-6
12. Prove that: (m+n)-1(m-1+n-1) = (mn)-1
Answer: LHS = 1/(m+n) × (1/m + 1/n) = 1/(m+n) × (n+m)/mn = 1/mn = (mn)-1 = RHS.
13. Prove that:
(i) (xa/xb)1/ab (xb/xc)1/bc (xc/xa)1/ca = 1.
Answer: x(a-b)/ab . x(b-c)/bc . x(c-a)/ca = x1/b - 1/a + 1/c - 1/b + 1/a - 1/c = x0 = 1.
(ii) 1/(1+xa-b) + 1/(1+xb-a) = 1
Answer: 1/(1 + xa/xb) + 1/(1 + xb/xa) = xb/(xb+xa) + xa/(xa+xb) = (xb+xa)/(xa+xb) = 1.
14. Find the value of n, when:
(i) 12-5 × 122n+1 = 1213 ÷ 127
Answer: 122n-4 = 126 => 2n-4 = 6 => 2n = 10 => n = 5.
(ii) [a2n-3 × (a2)n+1] / (a4)-3 = (a3)3 ÷ (a6)-3
Answer: a2n-3 + 2n+2 + 12 = a9 + 18 => a4n+11 = a27 => 4n = 16 => n = 4.
15. Simplify:
(i) [x2n+7 . (x2)3n+2] / x4(2n+3)
Answer: x2n+7 + 6n+4 / x8n+12 = x8n+11 / x8n+12 = x-1 = 1/x
(ii) [a2n+3 . a(2n+1)(n+2)] / [(a3)2n+1 . an(2n+1)]
Answer: a2n+3 + 2n2+5n+2 / a6n+3 + 2n2+n = a2n2+7n+5 / a2n2+7n+3 = a2
16. Evaluate :
(i) (2-3 + 3-2) × 70
Answer: (1/8 + 1/9) × 1 = 17/72
(ii) (80 + 2-1) × 32
Answer: (1 + 1/2) × 9 = 3/2 × 9 = 27/2 = 13.5
(iii) { (1/6)-1 - (1/5)-1 }-2
Answer: (6 - 5)-2 = 1-2 = 1
(iv) [ { (-1/3)-2 }2 ]-1
Answer: (-1/3)4 = (-3)4 is wrong. Power is -22-1 = 4. (-1/3)4 = 1/81.
(v) (5n+2 - 5n+1) / 5n+1
Answer: 5n+1(5 - 1) / 5n+1 = 4
17. Find the value of x, if:
(i) 1 / (125)x-7 = 52x-1
Answer: 5-3(x-7) = 52x-1 => -3x + 21 = 2x - 1 => 5x = 22 => x = 4.4
(ii) (2/3)3 × (2/3)-4 = (2/3)2x+1
Answer: 3 - 4 = 2x + 1 => -1 = 2x + 1 => 2x = -2 => x = -1
(iii) 4n ÷ 4-3 = 45
Answer: n - (-3) = 5 => n + 3 = 5 => n = 2
18. Simplify: (81 × 3n+1 - 9 × 3n) / (81 × 3n+2 - 9 × 3n+1)
Answer: (34 . 3n+1 - 32 . 3n) / (34 . 3n+2 - 32 . 3n+1) = (3n+5 - 3n+2) / (3n+6 - 3n+3) = 3n+2(33 - 1) / 3n+3(33 - 1) = 1/3
19. If 2n-7 × 5n-4 = 1250; find n.
Answer: 2n-7 × 5n-4 = 2 × 625 = 21 × 54. This doesn't match directly. Adjusting: 2n-7 × 5n-7+3 = 2n-7 × 5n-7 × 125 = (10)n-7 × 125 = 1250 => 10n-7 = 10 => n-7 = 1 => n = 8.
Test yourself
1. Multiple Choice Type:
Choose the correct answer from the options given below.
(i) The multiplicative inverse of (80 + 50)(80 - 50) is: (a) 0 (b) 49 (c) 1 (d) undefined
Answer: (d) undefined (as the expression equals (1+1)(1-1) = 0)
(ii) The value of [ (1/4)-2 + (1/3)-2 ] ÷ (1/5)-2 is: (a) 1/25 (b) 1 (c) 0 (d) 625 Answer: (b) 1
(iii) If 34 × 93 = 9n, then the value of n is: (a) 5 (b) 7 (c) 10 (d) none of the above
Answer: (a) 5 (34 = 92, so 92 × 93 = 95)
(iv) (5/6)5 × (6/5)-4 = (5/6)3x, then the value of x is: (a) 1/3 (b) 20/3 (c) -3 (d) 3
Answer: (d) 3
(v) (2/5)-8 ÷ (2/5)5 is equal to: (a) (2/5)-3 (b) (2/5)-13 (c) (2/5)13 (d) (5/2)-13
Answer: (b) (2/5)-13
(vi) Statement 1: (x0 + y0)(x + y)0 = 1, x, y ≠ 0. Statement 2: (1 + 1)(1 - 1) = 2 × 0 = 0 Which of the following options is correct? (a) Both the statements are true. (b) Both the statements are false. (c) Statement 1 is true, and statement 2 is false. (d) Statement 1 is false, and statement 2 is true.
Answer: (d) Statement 1 is false (it's 2), Statement 2 is true.
(vii) Assertion (A): (-100)3 = -10,00,000 Reason (R): (-p)q = pq; if q is even.
Answer: (b) Both are correct, but R is not explanation for A (A is odd case).
(viii) Assertion (A): (70 + 20)(70 - 20) = 0. Reason (R): Any number raised to the power zero(0) is always equal to 1.
Answer: (a) Both correct and R explains A.
(ix) Assertion (A): (1/5)-5 × (1/2)-5 = (10)-5 Reason (R): p-q = 1/pq and 1/p-q = pq, p ≠ 0.
Answer: (d) A is false (it's 105), R is true.
(x) Assertion (A): (p - q)-1(p-1 - q-1) = -(pq)-1 Reason (R): a-1 and a1 are multiplication reciprocal to each other.
Answer: (a) Both correct.
2. Evaluate:
(i) (-3/5)3
Answer: -27/125
(ii) (2/7)-2
Answer: 49/4
3. Evaluate : (-2/5)4 × (-5/2)2
Answer: (2/5)4 × (5/2)2 = (2/5)2 = 4/25
4. Evaluate : {(-1/2)-2}-3
Answer: (-1/2)6 = 1/64
5. Evaluate :
(i) (7-1 - 8-1) - (3-1 - 4-1)-1
Answer: (1/7 - 1/8) - (1/3 - 1/4)-1 = 1/56 - (1/12)-1 = 1/56 - 12 = -671/56
(ii) 5-7 ÷ 5-10 × 5-5
Answer: 5-7+10-5 = 5-2 = 1/25
6. By what number should (-5)-1 be divided to give the quotient (-25)-1
Answer: Let number be x. (-1/5) / x = -1/25 => x = (-1/5) / (-1/25) = 5.
7. Find n so that 811 ÷ 85 = 8-3 × 82n-1.
Answer: 6 = -3 + 2n - 1 => 6 = 2n - 4 => 2n = 10 => n = 5.
8. Find n so that 9n+2 = 240 + 9n
Answer: 9n(92 - 1) = 240 => 9n(80) = 240 => 9n = 3 => (32)n = 31 => 2n = 1 => n = 1/2.
9. Find x, if:
(i) 32x-1 = (27)x-3
Answer: 2x - 1 = 3(x - 3) => 2x - 1 = 3x - 9 => x = 8.
(ii) [25x × 55 × (125)3] / [5 × (625)4] = 125
Answer: [52x × 55 × 59] / [51 × 516] = 53 => 52x+14 - 17 = 53 => 2x - 3 = 3 => 2x = 6 => x = 3.