What percentage of the numbers from 1 to 70, both included, have 1 or 7 in the unit's digit?

Correct option is C

Given:

the percentage of numbers from 1 to 70 that have either 1 or 7 as the unit's digit.

Solution:

The numbers we are considering range from 1 to 70. 

Numbers ending in 1:These numbers are 1, 11, 21, 31, 41, 51, 61.

Numbers ending in 7: These numbers are 7, 17, 27, 37, 47, 57, 67.

Thus, there are 7 + 7 = 14 numbers that end in either 1 or 7.

The total number of integers from 1 to 70, inclusive, is 70.

​$$\text{Percentage} = \left( \frac{14}{70} \right) \times 100 = 20\%$$ 

​Thus the percentage of numbers from 1 to 70 that have 1 or 7 in the unit's digit is 20%.