Question

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 1

Hint: Number or ratio that can be expressed as a fraction of 100, which means, a part per hundred. The word percent means per 100. It is represented by the symbol “%”. Percentages have no dimension, hence are dimensionless numbers.
Formula used- $Percentage = \dfrac{{value}}{{total{\text{ value}}}} \times 100$

Complete step by step solution:
According to question,
We need to calculate the percentage of numbers from 1 to 70 that have 1 or 9 in the unit's digit.
As we know, from 1 to 10, there are 2 numbers which have 1 or 9 in the unit digit - 1 and 9. Similarly 2 numbers in 10-20. And so on. Hence there are 14 numbers which have unit digits as 1 or 9 between 1 to 70.
Total numbers - 70
Therefore, Total no. From 1 to 70 are 70…
Now, numbers with unit digit as 1 or 9 are as follows,
1,9,11,19,21,29,31, 39,….,61,69
We can sort the numbers as:
1,11,21,31,…,61 and 9,19,29,39,..,69
Now, we can find manually the required numbers. but in case we have many numbers, we can use some formulas of A.P.
In this case, we get 14 numbers…
Here, we use the percentage formula, which is basically used to find the amount or share of something in terms of 100.
The Percentage Formula is given as-
$Percentage = \dfrac{{value}}{{total{\text{ value}}}} \times 100$
Hence, percentage = $\dfrac{{14}}{{70}}$ ×100%
                                  =20%
Therefore, we have 20% of numbers from 1 to 70 have 1 or 9 in the unit's digit.
Thus, option(C) is the correct answer.

Note: The word percentage and percent are related closely to each other. Percent (or symbol %) is accompanied with a specific number. Example, more than 75% of the participants responded with their positive response to abjure. Percentage is represented without a number, is used generally for the general case of percent. Example, the percentage of the population affected by malaria is between 60% and 65%.