What is the mean of the first 11 prime numbers (correct to two decimal places)?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 14.55
List the primes in order starting from 2 (1 is not a prime), add them and divide by how many there are.
First 11 primes: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31
Sum \(=160\)
Mean \(=160\div11=14.5455\ldots\)
The mean is 14.55.
Why the other options are incorrect
Option (1) 17.73 — Incorrect. This leaves out 2, the only even prime, and takes the next 11 primes instead.
Option (2) 11.82 — Incorrect. This counts 1 as a prime; 1 is not a prime, so the first 11 primes run from 2 to 31.
Option (3) 16.00 — Incorrect. This divides the sum 160 by 10 instead of by 11.