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?

0 votes

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?

+1 vote

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.

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