If you wrote down all the numbers from 1 to 99 then how many times would you have written lsquo 7 ls...........

Quantitative Aptitude (CGL) Number System

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If you wrote down all the numbers from 1 to 99, then how many times would you have written ‘7‘?

This questions was previously asked in

SSC CGL 13 June 2019 Shift-3

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Explanation:

d1 = 5 − 2 = 3
d2 = 10 − 5 = 5
d3 = 17 − 10 = 7
d4 = 26 − 17 = 9
d5 = 37 − 26 = 11
d6 = 50 − 37 = 13
Total number in which 7 will occur at least once,is mentioned below,
7,17,27,37,47,57,67,77,87,97 - total 11 times 7 repeated.
70,71,72,73,74,75,76,78,79 - total 9 times 7 repeated
Hence total occurrence of 7 is 11+9=20

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