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1.
If 22n - 1 =
1
8n -3
, then the value of n is:  
  • A.
    3
  • C.
    0
  • B.
    2
  • D.
    - 2
  • Answer & Explanation
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Answer : [B]
Explanation :
 
22n - 1 =
1
8n - 3
 
22n - 1 =
1
(23)n -3
=
1
23(n -3)
=
1
2(3n - 9)
 = 2(9 - 3n)  
 
 
 
2n - 1 = 9 - 3n  
 
 
 
5n = 10  
 
 
 
n = 2  
 
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2.
(2.4 x 103) ÷ (8 x 10-2) = ?
  • A.
    3 x 10-5
  • C.
    3 x 105
  • B.
    3 x 104
  • D.
    30
  • Answer & Explanation
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Answer : [B]
Explanation :
 
(2.4 x 103) ÷ (8 x 10-2) =
2.4 x 103
8 x 10-2
=
24 x 102
8 x 10-2
 = (3 x 104)      
 
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3.
(18)3.5 ÷ (27)3.5 x 63.5 = 2? :
  • A.
    3.5
  • C.
    6
  • E.
    None of these
  • B.
    4.5
  • D.
    7
  • Answer & Explanation
  • Report
Answer : [D]
Explanation :
 
(18)3.5 ÷ (27)3.5 x 63.5 = 2x
 
 
  (18)3.5 x
1
(27)3.5
 x 63.5 = 2x  
 
 
  (32 x 2)3.5 x
1
(33)3.5
 x (2 x 3)3.5 = 2x  
 
 
  3(2 x 3.5) x 23.5 x
1
3(3 x 3.5)
 x 23.5 x 33.5 = 2x  
 
 
  37 x 23.5 x
1
310.5
 x 23.5 x 33.5 = 2x  
 
 
  27 x 2x  
 
 
  x = 7  
 
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4.
Number of prime factors in
612 x (35)28 x (15)16
(14)12 x (21)11
 is :  
  • A.
    56
  • C.
    112
  • B.
    66
  • D.
    None of these
  • Answer & Explanation
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Answer : [B]
Explanation :
 
 
612 x (35)28 x (15)16
(14)12 x (21)11
=
(2 x 3)12 x (5 x 7)28 x (3 x 5)16
(2 x 7)12 x (3 x 7)11
     
 
  =
212 x 312 x 528 x 728x 316 x 516
212 x 712 x 311 x 711
 
 
  = 2(12 - 12) x 3(12 + 16 - 11) x 5(28 + 16) x 7(28 - 12 - 11)  
 
  = 20 x 317 x 544 x 7-5  
 
  =
317 x 544
75
   
 
Number of prime factors = 17 + 44 + 5 = 66.
 
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5.
If 2n - 1 + 2n + 1 = 320, then n is equal to:
  • A.
    6
  • C.
    5
  • B.
    8
  • D.
    7
  • Answer & Explanation
  • Report
Answer : [D]
Explanation :
 
 
  2n - 1 + 2n + 1 = 320  
 
 
  2n - 1 (1 + 22) = 320  
 
 
  5 x 2n - 1 = 320  
 
 
  2n - 1 =
320
5
 = 64 = 26    
 
 
  n - 1 = 6  
 
 
  n = 7  
 
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