Multiple choice

The average marks of 20 students in a test is 75. Later it is found that three marks 53, 60 & 76 were wrongly entered as 93, 64 & 86. The average marks after mistakes were rectified is

  1. 72.3

  2. 72.2

  3. 71.6

  4. 71.8
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Original sum = 20 × 75 = 1500. Wrongly entered marks: 93 + 64 + 86 = 243. Correct marks: 53 + 60 + 76 = 189. Corrected sum = 1500 − 243 + 189 = 1446. Corrected average = 1446 ÷ 20 = 72.3. The net decrease is (243 − 189) ÷ 20 = 2.7, so 75 − 2.7 = 72.3.

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