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  • Question
  • 1/(1 x 4) + 1/(4 x 7) + 1/(7 x 10) + 1/(10 x 13) + 1/(13 x 16) =?


  • Options
  • A. 5/16
  • B. 3/16
  • C. 7/16
  • D. 11/16

  • Correct Answer
  • 5/16 

    Explanation

    Given expression can be written as
    = 1/(1 x 4) + 1/(4 x 7) + 1/(7 x 10) + 1/(10 x 13) + 1/(13 x 16)
    = 1/3{ 3/(1 x 4) + 3/(4 x 7) + 3/(7 x 10) + 3/(10 x 13) + 3/(13 x 16) }
    = 1/3{ (4 - 1)/(1 x 4) + (7 - 4)/(4 x 7) + (10 - 7 )/(7 x 10) + (13 - 10)/(10 x 13) + (16 - 13/(13 x 16) }
    = 1/3[(1 - 1/4) + (1/4 - 1/7) + (1/7 - 1/10) + (1/10 - 1/13) + (1/13 - 1/16)]
    = 1/3[1 - 1/4 + 1/4 - 1/7 + 1/7 - 1/10 + 1/10 - 1/13 + 1/13 - 1/16]
    = 1/3[1 - 1/16]
    = 1/3[ (16 - 1)/16]
    = 1/3[ (15)/16]
    = 1 x 15/ 3 x 16
    = 5/16


  • More questions

    • 1. 
      The product of two consecutive odd numbers is 19043. Which is the smaller one?

    • Options
    • A. 137
    • B. 131
    • C. 133
    • D. 129
    • Discuss
    • 2. 
      The angle of elevation of the top of a hill from each of the vertices A, B, C of a horizontal triangle is ?. The height of the hill is :

    • Options
    • A. b tan ? cosec B
    • B. a tan ? cosec A 2
    • C. c tan ? cosec C 2
    • D. None of these
    • Discuss
    • 3. 
      From a point on a circular tract 5 Km long A, B and C started running in the same direction at the same time with speeds of 2 1? 2 Km/h, 3 Km/h and 2 Km/h. respectively. Then on the starting point all three will meet again after :

    • Options
    • A. 30 hours
    • B. 6 hours
    • C. 10 hours
    • D. 15 hours
    • Discuss
    • 4. 
      The radius of the wheel of a vehicle is 70 cm. The wheel makes 10 revolutions in 5 seconds. The speed of the vehicle is?

    • Options
    • A. 29.46 km/hr.
    • B. 31.68 km/hr.
    • C. 36.25 km/hr.
    • D. 32.72 km/hr.
    • Discuss
    • 5. 
      A library has two books each having three copies and three other books each having two copies. In how many ways can all these books be arranged in a shelf so that copies of the same book are not separated?

    • Options
    • A. 120
    • B. 180
    • C. 160
    • D. 140
    • Discuss
    • 6. 
      Find the LCM of 1/3, 2/9, 5/6 and 4/27.

    • Options
    • A. 1/54
    • B. 10/27
    • C. 20/3
    • D. 3/20
    • Discuss
    • 7. 
      A runs 1 3? 8 times as fast as B. If A gives B a start of 120 m and they reach the goal at the same time, the goal is at a distance of:

    • Options
    • A. 360 m
    • B. 440 m
    • C. 460 m
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    • Discuss
    • 8. 
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    • Options
    • A. 2000
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    • Discuss
    • 9. 
      Given that log 10 2 = 0.3010 the value of log 10 5 is?

    • Options
    • A. 0.3241
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    • Discuss
    • 10. 
      In a month of 31 days, third Thursday falls on 16th. What will be the last day of the month?

    • Options
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