the sum of 7 consecutive integers is 980 . how many of them are prime ?  Choose the correct choice from the following options: A) 0 B) 1 C) 2 D) 3 E) 4

Rationale: the middle number is 140 and the seven numbers are 137 , 138 , 139 , · · · , 143 . now 138 , 140 , and 142 are even , 141 is divisible by 3 , and 143 - by 11 . the remaining numbers 137 and 139 are prime ( it is easy to check that they are not divisible by 23 , 57 and 11 ) . correct answer c
Answer: C