How much had Tarun scored in Math?

Question

Tarun came second in Math. When his mother asked him how much he had scored, he answered that he got the sum of the first 9 even numbers. His mother immediately worked out the answer.
How much had he scored in Math?

Answer 1

72 or 90 depending
on whenever zero or
two comes first.

Answer 2

An even number is represented by '2n' in Algebra. The first nine even numbers are represented as follows
2n =1, where n=1
2*2n = 4,
4*2n = 6. Continuing in this way the sum of first nine even numbers will be,
2n+2*2n+4*2n+6*2n _ ...9*2n = 2n[1+2+3+4+5...9] = 2n X n (n+1) = 2n*9x10/2 = 2n * 45. Assume the value of 'n' to be 1. Substituting this value we get, 45*2 = 90. So Tarun's marks in Mathematics is 90. M J SUBRAMANYAM, BENGALURU.