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:
101 comments Page 1 of 11.
Karthik said:
1 decade ago
Any short cut for this?
Syed said:
1 decade ago
Ya there is a short cut the concept is :
Let's look for the no. whose square ends with 1 from 1-10, we will find that there are only two such number that is 1 and 9. That is between 1-70 there will be 14 such number.
Now lets find the percentage. 14 is what percent of 70.
10% of 70 is 7
Therefore 20% of 70 will be 2 * 7 = 14 the answer is 20%.
Let's look for the no. whose square ends with 1 from 1-10, we will find that there are only two such number that is 1 and 9. That is between 1-70 there will be 14 such number.
Now lets find the percentage. 14 is what percent of 70.
10% of 70 is 7
Therefore 20% of 70 will be 2 * 7 = 14 the answer is 20%.
Chandrakala said:
1 decade ago
What about 4? 4 is also squre, so 4, 24, 34, 44, 54, 64 also have squre that end in the digit 1.
Priya P. said:
1 decade ago
@chandrakala
Its not end in 1 digit, its end with digit 1
as (1)^2=1
(9)^2=81 ;8(1)
got it..
Its not end in 1 digit, its end with digit 1
as (1)^2=1
(9)^2=81 ;8(1)
got it..
Saranya said:
1 decade ago
Thank you for your short cut syed.
Ross said:
1 decade ago
I see that number 10 is not included into consideration even though it has 1 in its digit unit, why?
Pankaj said:
1 decade ago
Very good priya.
PANKAJ said:
1 decade ago
@ ROSS
The no 10 after squaring it does not end with 1.......
if u square to 1,11,19,21 it ends with 1
Squaring 10 = 10 x 10 = 100 it ends with 0
Squaring 11 = 11 x 11 = 121 it ends with 1
I think u got it.
The no 10 after squaring it does not end with 1.......
if u square to 1,11,19,21 it ends with 1
Squaring 10 = 10 x 10 = 100 it ends with 0
Squaring 11 = 11 x 11 = 121 it ends with 1
I think u got it.
Gopal said:
1 decade ago
@pankaj.
It is wrong method unit digit means endshould be 1 or 9.
And 10 will be end in 0 so 10 is not include.
It is wrong method unit digit means endshould be 1 or 9.
And 10 will be end in 0 so 10 is not include.
Uttam said:
1 decade ago
Inside the 10 there are 2 digits which ends with 1 and 9.
Number 70 consists 7 tens.
So total no of digits that end with 1 and 9 in 70 are,
7*2=14.
So percentage= (14/70) *100=20.
Number 70 consists 7 tens.
So total no of digits that end with 1 and 9 in 70 are,
7*2=14.
So percentage= (14/70) *100=20.
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