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Home Aptitude Height and Distance See What Others Are Saying!
  • Question
  • On the ground level the angle of elevation of the top of a tower is 30°, On moving 20 m nearer the tower, the angle of elevation found to be 60°. The height of the tower is?


  • Options
  • A. 10 m
  • B. 10?3 m
  • C. 15 m
  • D. 20 m

  • Correct Answer
  • 10?3 m 

    Explanation

    Let us draw a figure below from the given question.
    Let AB = h meter be the height of the towers. B and C are two points such that BC = 20 m; ?ADB = 30° and ?ACB = 60° BC = x meter (let us assume)
    Now, from right triangle ABC,
    x = h cot 60°
    ? x = h/?3 meter
    Again, from right triangle ABD,
    h = (20 + x) tan 30°
    put the value of x in above equation.
    ? x = h/?3
    ? h = (20 + h/?3) x 1/?3 ( ? tan 30° = 1/?3 )
    ? h - h/3 = 20/?3 ? 2h/3 = 20/?3
    ? h = 20 x 3/2?3 = 10?3 m


  • More questions

    • 1. 
      0.0169 / 0.013=?

    • Options
    • A. .13
    • B. .013
    • C. 1.3
    • D. 13
    • Discuss
    • 2. 
      Two posts are x meter apart and the height of one is double that of the other. If from the midpoint of the line joining their feet, an observer finds the angular elevations of their tops to be complementary, then the height (in meter) of the shorter post is :

    • Options
    • A. x 2 ?2
    • B. x 4
    • C. x ?2
    • D. x ?2
    • Discuss
    • 3. 
      If p/q =4/5, then the value of 4/7 + {(2q - p) / (2q + p)} is?

    • Options
    • A. 3 / 7
    • B. 34
    • C. 1
    • D. 2
    • Discuss
    • 4. 
      What is 25% of 25% is equal to?

    • Options
    • A. 6.25
    • B. .625
    • C. .0625
    • D. .000625
    • Discuss
    • 5. 
      The number .05 is hoe many percent of 20?

    • Options
    • A. 25
    • B. .025
    • C. .25
    • D. 2.5
    • Discuss
    • 6. Find the lowest common multiple of 24, 36 and 40.

    • Options
    • A. 120
    • B. 240
    • C. 360
    • D. 480
    • Discuss
    • 7. 
      8 1/ 3% expressed as a fraction is?

    • Options
    • A. 25/3
    • B. 3/25
    • C. 1/12
    • D. 1/4
    • Discuss
    • 8. 
      .025 in terms of term of rate per cent is?

    • Options
    • A. .25%
    • B. 2.5%
    • C. 0.25%
    • D. 371/2%
    • Discuss
    • 9. 
      What percentage of 2/7 is 1/35?

    • Options
    • A. 2.5%
    • B. 10%
    • C. 25%
    • D. 20%
    • Discuss
    • 10. 
      A sum of ? 4000 is lent out in two parts, one at 8% simple interest and other at 10% simple interest. If the annual interest is ? 352, the sum lent at 8% is

    • Options
    • A. ? 1600
    • B. ? 2400
    • C. ? 1800
    • D. ? 2800
    • Discuss


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