MCQ practice · SSC General Mathematics Board questions · Chapter 17: Statistics
What is the arithmetic mean of the primes from 1 to 19?
Think it through first, then pick an option.
- a 11.00
- b 10.57
- c 9.75
- d 9.63
Answer and explanation
Correct answer: d 9.63
(2 + 3 + 5 + 7 + 11 + 13 + 17 + 19)/8 = 77/8 = 9.625 ≈ 9.63.
Why the other options are wrong
- a 11.00: 77 ÷ 7 = 11 miscounts; there are eight primes.
- b 10.57: 10.57 is a slip from leaving a prime out of the count.
- c 9.75: 9.75 = 78 ÷ 8 would need a sum of 78; the true sum is 77.
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