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:
103 comments Page 11 of 11.
Chandrakala said:
2 decades ago
What about 4? 4 is also squre, so 4, 24, 34, 44, 54, 64 also have squre that end in the digit 1.
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%.
Karthik said:
2 decades ago
Any short cut for this?
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