The prime numbers between 20 and 140 are:
23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109,
113, 119, 127, 131, 137 and 139
(b) Which two groups of three consecutive prime numbers, between 10 and 50, have
a sum which is not prime?
Answer: ———— + ———— + ———— = ————
———— + ———— + ———— = ————