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How much had Tarun scored in Math?

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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?

posted Aug 6, 2015 by Mridul

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2 Answers

+2 votes

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

answer Aug 7, 2015 by anonymous
+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.

answer Aug 8, 2015 by anonymous

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