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:
2%
2.02%
4%
4.04%
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 1 of 4.

Ramesh said:   1 decade ago
Sir Percentage error is not understanding. Please solve the answer.

Sakshi said:   1 decade ago
We can also get the percentage by this.

Percentage error = 404/100 = 4.04

Anbu said:   1 decade ago
(A2 - A1) = [(102)2 - (100)2] How it come?

Please advise

Amrita said:   1 decade ago
To find out error we got to subtract it first.

Shreya singh said:   1 decade ago
In this type of % some usefull idea is to take default no as 100 and in question 2% is error. Hence our no is 100 error no is 102.

So solve further with square formula:

Area= (side)* (side)

Mazher said:   1 decade ago
Why we are taking this three 100's ?

Meghna said:   1 decade ago
@anbu.
Take the formula a^2-b^2
which is equal to (a+b)(a-b) ... so (102-100)(102+100)

Shikha said:   1 decade ago
Why are we dividing 401 by 100 two times and not one time?

Why it is not- (401*100) /100?

Pradyumna said:   1 decade ago
@Sikha.

That is (404*100) /(100*100).
Because we are finding the %error.
Where 404 is change in area and (100*100) for original area.

Hasini said:   1 decade ago
Correct area = (100)^2.

Measured area = (102)^2.

So to get the excess area we have to subtract the incorrectly measured area by the correct area.

(102)^2-(100)^2.

(102+100)(102-100) .

202*2.

= 404.

So, 404/100.

= 4.4%.


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