(a) Sum of 3 consecutive numbers = 3 × middle number = $3 \times 68$ = 204. (b) Sum of 4 consecutive numbers = 2 × (middle two sum) = 2 × (25 + 26) = $2 \times 51$ = 102. Or: $4 \times 25.5$ = 102. (c) Sum of 5 consecutive numbers = 5 × middle number = $5 \times 50$ = 250. (d) Sum of 6 consecutive numbers = 3 × (first + last) = 3 × (237 + 242) = $3 \times 479$ = 1,437.