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What percentage of numbers from 1 to 70 have 1 or 9 in the unit’s digit?

a) 1%
b) 14%
c) 20%
d) 21%

Answer: c
Explanation: The numbers which have 1 or 9 in the unit’s digit, have squares that end in the digit 1.
Such numbers from 1 to 70 are 1, 9, 11, 19, 21, 29, 31, 39, 41, 49, 51, 59, 61, 69.
Number of such number = 14
$$ = \left( {\frac{{14}}{{70}} \times 100} \right)\% = 20\% $$

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