Aptitude - Percentage - Discussion

To find the percentage of numbers from 1 to 70 that have 1 or 9 in the unit's digit, we first identify all such numbers.

Numbers with 1 in the unit's digit:
1, 11, 21, 31, 41, 51, 61

Numbers with 9 in the unit's digit:
9, 19, 29, 39, 49, 59, 69

Each set has 7 numbers.

Combining both sets, we have:
1, 9, 11, 19, 21, 29, 31, 39, 41, 49, 51, 59, 61, 69,
In total, there are 14 numbers from 1 to 70 with either 1 or 9 in the unit's digit.

Percentage = ( Number of desired numbers)/Total numbers × 100.
Percentage = (14/70)× 100 = 20%.
Therefore, 20% of the numbers from 1 to 70 have either 1 or 9 in the unit's digit.

!All.

Here, They asked 1 or 9, why all answers are included both 1 and 9, if we considered 1 or 9 only the percentage should be 10%.

Correct me, if I'm wrong.

@All.

Here is my explanation for the answer.

Let's take initial values as 100%, which means initially the fruit seller had some apples, so I take that as 100%.

Now, if he sells 40% of his apples, he has 60% of the apples remaining.

So, in the question, they have already stated that the seller has 420 apples after selling 40%.

Thus, we have:
60% = 420.
100% = x.

To solve this expression:
x = (420×100)60x = 60(420×100)​.
x = 700x = 700.

Therefore, the answer is 700.

1 to 9 = 2 digit (1,9) =2.
11 to 70 = [digit1-tens digit2-units].
At unit one place suppose I have put 1 there that means I have the choice to
put 6 digits at the tens place = 6 * 1 = 6.
similarily for 9 also = 6 *1 = 6.

The reason we are taking 6 digits is because it will exceed the range that is given.
So, total = 14,
14 = x /100 * 70,
x = 20%.

@Moses Ug.

We can't consider 12 to 18 because the question says in units place of a number it should either have 1 or 9 not in tens place.

Why shouldn't we consider 10, 11, 12, 13, 14, 15, 16, 17, 18 as they have 1 in its unit?

Numbers from 1 to 70.
Having 1 or 9 in unit digits,
1 seven times and 9 seven times,
14/70 * 100 = 20.

Does 12 up to 18 have a digit 1 or not?

Anyone, please clarify.

Very helpful explanation, Thanks. @Tabi.

@Lobsang.

Because, They didn't ask about us anyone's Square.

They just told you to find how many no belongs in 1to70 That last digit should come only 1 and 9. Like 01, 09, 11, 19, 21, 29. 69.

Hope you understood.