Answer:
(E) 83
Step-by-step explanation:
So f(x) is the sum of all prime numbers less than x.
So f(86) is the sum of all prime numbers less than 86:
f(86) = 2 + 3 + 5 + 7 + 11 + 13 + 17 + 19 + 23 + 29 + 31 + 37 + 41 + 43 + 47 + 53 + 59 + 61 + 67 + 71 + 73 + 79 + 83
= 874
Likewise, f(82) is the sum off all prime numbers less than it, which would be;
f(82) = 2 + 3 + 5 + 7 + 11 + 13 + 17 + 19 + 23 + 29 + 31 + 37 + 41 + 43 + 47 + 53 + 59 + 61 + 67 + 71 + 73 + 79
= 791
The problem asks us to do:
f(86) - f(82)
Substitute for numerical values:
874 - 791
solve
= 83
