Question
The sum of all the 2-digit numbers is :
Answer: Option D
Answer: (d)The two-digit numbers are : 10, 11, 12, ..... 97, 98, 99We know that, 1+ 2 + 3 + 4 + ..... + n = ${n(n+1)}/2$Required sum = (1 + 2 + 3 + ......+ 99)-(1+2+ ..... + 9) = ${99 (99 + 1)}/2 - {9(9 + 1)}/2$= 4950 – 45 = 4905
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Answer: (d)The two-digit numbers are : 10, 11, 12, ..... 97, 98, 99We know that, 1+ 2 + 3 + 4 + ..... + n = ${n(n+1)}/2$Required sum = (1 + 2 + 3 + ......+ 99)-(1+2+ ..... + 9) = ${99 (99 + 1)}/2 - {9(9 + 1)}/2$= 4950 – 45 = 4905
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