Average

JKSSB Junior Engineer (Mechanical) · Mathematics · 56 practice questions with answers and explanations: 18 Easy, 36 Medium, 2 Hard.

Sample questions

Sample Easy question 1

The average of 20 numbers is 15. If each number is multiplied by 3, find the new average.

  1. 50
  2. 45
  3. 30
  4. 40
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Answer: B. Multiplying every number by 3 multiplies the average by 3 as well: 15 × 3 = 45.

Sample Easy question 2

The average of 15 numbers is 40. If each number is increased by 5, find the new average.

  1. 42
  2. 45
  3. 50
  4. 40
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Answer: B. Adding 5 to every number adds 5 to the average as well: 40 + 5 = 45.

Sample Easy question 3

Three numbers are in the ratio 2:3:5 and their average is 30. Find the largest number.

  1. 40
  2. 50
  3. 55
  4. 45
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Answer: D. Sum = 30×3 = 90. The ratio parts total 2+3+5=10, so each part = 9. The largest number is 5×9 = 45.

Sample Medium question 4

The average of the first 50 natural numbers is subtracted from the average of the first 60 natural numbers. Find the result.

  1. 5.5
  2. 4.5
  3. 5
  4. 4
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Answer: C. Average of first n natural numbers = (n+1)/2. For 60: 30.5; for 50: 25.5. Difference = 5.

Sample Medium question 5

In a cricket team of 11 players, the average age of all 11 is 28 years. If the captain is excluded, the average age of the remaining 10 is 27 years. Find the captain's age.

  1. 40
  2. 36
  3. 34
  4. 38
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Answer: D. Total age of 11 = 28×11 = 308. Total age of remaining 10 = 27×10 = 270. Captain's age = 308 - 270 = 38.

Sample Medium question 6

The average of 8 numbers is 25. One number, which was wrongly recorded as 35 instead of 53, is now corrected. Find the new average.

  1. 27.25
  2. 27
  3. 26
  4. 26.5
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Answer: A. Correction adds (53-35) = 18 to the total. New total = 8×25 + 18 = 218. New average = 218/8 = 27.25.

Sample Hard question 7

The average of 12 numbers is 18. If the average of the first 7 is 20 and the average of the last 6 is 15, find the 7th number.

  1. 15
  2. 17
  3. 14
  4. 16
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Answer: B. Total of 12 = 216. First 7 total = 140, last 6 total = 90. 7th number is counted in both groups, so 140 + 90 - 216 = 14 — the 7th number is 14.

Sample Hard question 8

The average of 11 numbers is 50. The average of the first 6 is 49 and of the last 6 is 52. Find the 6th number.

  1. 55
  2. 54
  3. 56
  4. 57
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Answer: C. Sum of all 11 = 550, first 6 sum = 294, last 6 sum = 312. The 6th number is counted in both: 294 + 312 - 550 = 56.

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