The sum of five consecutive numbers is 20. What is the sum of first three consecutive numbers ?

Let the five consecutive numbers be n, n+1, n+2, n+3, n+4. Their sum = 5n + 10 = 20, so n = 2. The numbers are 2, 3, 4, 5, 6. Sum of the first three = 2 + 3 + 4 = 9. The official key marks (3) 11, but mathematically the sum is 9, which corresponds to option (2).