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:
102 comments Page 3 of 11.
Tabi said:
9 years ago
Look again for the definition of "unit's digit".
If we have (for the sake of example) --> 180.
Then:
1 on '1'80 = hundreds digit.
8 on 1'8'0 = tens digit.
0 on 18'0' = units digit.
Therefore, numbers that fulfill the question "What percentage of numbers from 1 to 70 have 1 or 9 in the unit's digit?" is numbers that have either '1' or '9' on its "units digit".
Disclaimer: 10, or 12, 13, 14, 15, 16, 17 and 18 did not make it to the answer because even though they have '1' on its component, that '1'is not a "units digit" since our definition above.
The correct numbers are: 1, 9 , 11, 19, 21, 29 , 31, 39, 41, 49, 51, 59, 61, 69.
*Counted -> 14 numbers out of 70's.
Percentage = (14/70)*100% = 20%.
Answer : C
If we have (for the sake of example) --> 180.
Then:
1 on '1'80 = hundreds digit.
8 on 1'8'0 = tens digit.
0 on 18'0' = units digit.
Therefore, numbers that fulfill the question "What percentage of numbers from 1 to 70 have 1 or 9 in the unit's digit?" is numbers that have either '1' or '9' on its "units digit".
Disclaimer: 10, or 12, 13, 14, 15, 16, 17 and 18 did not make it to the answer because even though they have '1' on its component, that '1'is not a "units digit" since our definition above.
The correct numbers are: 1, 9 , 11, 19, 21, 29 , 31, 39, 41, 49, 51, 59, 61, 69.
*Counted -> 14 numbers out of 70's.
Percentage = (14/70)*100% = 20%.
Answer : C
(1)
Laxman said:
7 years ago
In question there should be 1 & 9 instead of 1 or 9.
(1)
Ganesh said:
7 years ago
Simple 1 or 9 in unit digit in 1st 10 no. Is 2,
So 1 to 70 = 2*7 = 14.
% = 14/70*100 = 20% Answer.
So 1 to 70 = 2*7 = 14.
% = 14/70*100 = 20% Answer.
(1)
Sanjana said:
7 years ago
Digits with 1 in unitary place:7.
Digits with 9 in unitary place:7.
7+7=14,
The total numbers=70.
14/70*100=140/7=20%.
Digits with 9 in unitary place:7.
7+7=14,
The total numbers=70.
14/70*100=140/7=20%.
(1)
LOBSANG said:
3 years ago
Then why don't we consider 7 here because it also ends with 9 as a unit digit 7*7=49?
Anyone clarify it.
Anyone clarify it.
(1)
Ankush kushwaha said:
1 year ago
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%.
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%.
(1)
Karthik said:
2 decades ago
Any short cut for this?
Syed said:
2 decades 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..
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