Aptitude - Percentage - Discussion

@Jim.

The unit digit is the ending digit.

Why don't we consider the 12, 13, 18 because it has 1 as a unit digit?

What is the unit's digit? Please explain me.

In every ten numbers, we have only two numbers that end with digits 1 or 9.
So b/w 1 to 70 we 14. (7*2 = 14).
Here 7 represents no of tens and 2 represents no of numbers that end with digit 1 or 9.
So, 14/70 * 100 = 20.

The question is not talking about ending with 1 or 9, but it's talking about numbers having 1 or 9.

@Shubham.

12^2 = 144 here, the last digit in 144 is four not "1" that's y 12 is not being taken.

Therefore, if the number with the last digit 1 and it's square the last digit is 1 is not being taken!
And it's the same with the other number like 13, 17.. and all!!

Got it?

Why 12, 13... 17 has not considered? Please tell me.

@Muskan and @Preethy.

It is being ask the percentage in two conditions:

a) the number should be between 1 to 70.
b) the number selected between 1 to 70, it's square should have digit 1 at the end.

In simple words, for example the number 11 which consists of digit 1 which satisfies the condition (a) and also it's square (i.e) 121 is also having 1 at end which also satisfies the condition (b) so, this number is taken.

Whereas, if we take number 15 which consists of digit 1 in it but it's square (i.e) 225 is not having digit 1 at the end, therefore, it won't be taken.

And that how the numbers 1,9,11,19,21,29,31,39,41,49,51,59,61,69 are taken which are 14 in total.

Therefore, 14/70 * 100 = 20.

I am not understanding the answer, please explain it.

I am not understanding, please anyone explain me.