Aptitude - Percentage - Discussion
Discussion Forum : Percentage - General Questions (Q.No. 4)
4.
What percentage of numbers from 1 to 70 have 1 or 9 in the unit's digit?
Answer: Option
Explanation:
Clearly, 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
 Required percentage = |
 |
14 | x 100 |  % = 20%. |
| 70 |
Video Explanation: https://youtu.be/cBamI6iRNIA
Discussion:
107 comments Page 11 of 11.
Sanjana said:
7 years ago
@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.
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.
Shubham matekar said:
7 years ago
Why 12, 13... 17 has not considered? Please tell me.
Sanjana said:
7 years ago
@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?
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?
Jim said:
7 years ago
The question is not talking about ending with 1 or 9, but it's talking about numbers having 1 or 9.
Arushi said:
6 years ago
@Jim.
The unit digit is the ending digit.
The unit digit is the ending digit.
Villan said:
6 years ago
The simplest method is by counting the unit places as 3 and 7.
So, there are 14 nos.
14/70*100=20 %.
So, there are 14 nos.
14/70*100=20 %.
Anand said:
2 weeks ago
To find the percentage of numbers from 1 to 70.
Let's say 1-70 = 100%.
So in there, we want the percentage of 1 and 9 numbers, so we just have to do.
Every 1-70 has 1, and every 1-70 has 9.
So if 1-70 = 100%, 1 is 10% and 9 is 10%, and we sum the percentages, we get 10+10 = 20% answer.
Let's say 1-70 = 100%.
So in there, we want the percentage of 1 and 9 numbers, so we just have to do.
Every 1-70 has 1, and every 1-70 has 9.
So if 1-70 = 100%, 1 is 10% and 9 is 10%, and we sum the percentages, we get 10+10 = 20% answer.
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