Aptitude - Area - Discussion
Discussion Forum : Area - General Questions (Q.No. 2)
2.
An error 2% in excess is made while measuring the side of a square. The percentage of error in the calculated area of the square is:
Answer: Option
Explanation:
100 cm is read as 102 cm.
A1 = (100 x 100) cm2 and A2 (102 x 102) cm2.
(A2 - A1) = [(102)2 - (100)2]
= (102 + 100) x (102 - 100)
= 404 cm2.
| Percentage error = |
 |
404 | x 100 |  % |
= 4.04% |
| 100 x 100 |
Discussion:
40 comments Page 2 of 4.
Arpita said:
8 years ago
But it isn't given that error is made and the length is increased by 2cm.
I mean 2%of 100 = 2.
But then we can even subtract 2 from 100 which us 98 instead of adding that 2.
Please help me.
I mean 2%of 100 = 2.
But then we can even subtract 2 from 100 which us 98 instead of adding that 2.
Please help me.
Sakshi said:
9 years ago
Please explain the last step of the solution.
Raju said:
9 years ago
The formula X + Y + (X * Y/100) is the best for square and rectangle.
Bhavna said:
9 years ago
2% is the excess
Let say area is 100 cm.
Therefore,
Wrong area is 100 + 2 cm.
Right area is 100 cm.
Wrong - Right = (102)^2 - (100)^2.
404.
Error is - (excess/total area) i.e. 404/100 which gives 4.04
Now you can find the percentage by multiplying and dividing by 100.
Ans -> 4.04%
Let say area is 100 cm.
Therefore,
Wrong area is 100 + 2 cm.
Right area is 100 cm.
Wrong - Right = (102)^2 - (100)^2.
404.
Error is - (excess/total area) i.e. 404/100 which gives 4.04
Now you can find the percentage by multiplying and dividing by 100.
Ans -> 4.04%
Pranjal said:
9 years ago
The formula X + Y + (X*Y/100) is the best for square and rectangle.
(1)
Danah Bader said:
9 years ago
Exactly @Harsh.
The method is wrong!
I don't seem to understand the reason why this is wrong?
The method is wrong!
I don't seem to understand the reason why this is wrong?
Abhishek Maurya said:
10 years ago
Percentage error = X+Y+(XY)/100.
So, => 2+2+(2*2)/100.
= 4.04.
Note : This method valid for only two values.
So, => 2+2+(2*2)/100.
= 4.04.
Note : This method valid for only two values.
Harsh said:
10 years ago
@Mahesh,
Difference in the area is indeed 101 but you must not divide it by 100. The area for your square was 2500 (50*50) and multiplying this by 100 (for percentage) gives you (101/2500)*100 = 4.04.
Difference in the area is indeed 101 but you must not divide it by 100. The area for your square was 2500 (50*50) and multiplying this by 100 (for percentage) gives you (101/2500)*100 = 4.04.
Harsh said:
10 years ago
Why is this method wrong?
A = a^2;
dA = 2*a*da;
dA/A = 2*(da/a).
We know da/a = 2%. Hence, dA/A = 4%.
I don't seem to understand the reason why this is wrong? Can someone explain?
A = a^2;
dA = 2*a*da;
dA/A = 2*(da/a).
We know da/a = 2%. Hence, dA/A = 4%.
I don't seem to understand the reason why this is wrong? Can someone explain?
(1)
Mahesh said:
1 decade ago
Why you all are consider side of the square is 100.
If we are tack original side of the square is 50.
2% error so side is 50*2/100 = 1. So side of square is 51.
= (51)^2 - (50)^2 = (51+50) (51-50) = 101/100 = 1.01 answer.
Please explain me.
If we are tack original side of the square is 50.
2% error so side is 50*2/100 = 1. So side of square is 51.
= (51)^2 - (50)^2 = (51+50) (51-50) = 101/100 = 1.01 answer.
Please explain me.
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