Aptitude - Area - Discussion
Discussion Forum : Area - General Questions (Q.No. 7)
7.
A towel, when bleached, was found to have lost 20% of its length and 10% of its breadth. The percentage of decrease in area is:
Answer: Option
Explanation:
Let original length = x and original breadth = y.
| Decrease in area |
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 Decrease % = |
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7 | xy x | 1 | x 100 |  % |
= 28%. |
| 25 | xy |
Discussion:
28 comments Page 2 of 3.
Sreelu said:
9 years ago
There is another simple method.
Let's assume L = 10 and B = 10.
Then area will be 100 (L * B).
When L lost 20% it gets the value 8.
Like that, B lost 10% it gets the value of 9.
So, the new area is 72 i.e (8 * 9).
Then % decrease = 100 - 72 = 28.
Let's assume L = 10 and B = 10.
Then area will be 100 (L * B).
When L lost 20% it gets the value 8.
Like that, B lost 10% it gets the value of 9.
So, the new area is 72 i.e (8 * 9).
Then % decrease = 100 - 72 = 28.
(1)
Islam Ansari said:
9 years ago
xy - 18/25xy.
= 7/25xy.
How?
= 7/25xy.
How?
Sam said:
9 years ago
x + y - (x * y/100).
Then, 20% + 10% - [20 * 10/100].
30% - 2% = 28%.
Then, 20% + 10% - [20 * 10/100].
30% - 2% = 28%.
Sriram said:
1 decade ago
So simple by a formula.
x% decrease in length y% decrease in breadth then area change is -x-y+(x*y)/100.
x% decrease in length y% decrease in breadth then area change is -x-y+(x*y)/100.
(1)
Kunal said:
1 decade ago
It can also solve by percentage rule.
Suppose a towel area is 100 decreases by 20% and then 10%.
The are of towel= 100 of 20%=20 (say a).
Then, 80 of 10%=8 (say b).
Towels area=a+b.
20+8 = 28% answer.
Suppose a towel area is 100 decreases by 20% and then 10%.
The are of towel= 100 of 20%=20 (say a).
Then, 80 of 10%=8 (say b).
Towels area=a+b.
20+8 = 28% answer.
Harsha said:
1 decade ago
A1 = 100*100 = 10000 (ORIGINAL AREA).
A2 = 80*90 = 7200 (DECREASED IN AREA).
A2-A1 = 2800.
(A2-A1)% = 28%.
A2 = 80*90 = 7200 (DECREASED IN AREA).
A2-A1 = 2800.
(A2-A1)% = 28%.
Samuel said:
1 decade ago
It can also be solved as thus. Reduction in length = 100 - 20 = 80% which is 80/100.
Reduction in width= 100 - 10 = 90%.
Which is 90/100.
80/100* 90/100* 100 = 72.
100 - 72 = 28%.
Reduction in width= 100 - 10 = 90%.
Which is 90/100.
80/100* 90/100* 100 = 72.
100 - 72 = 28%.
Manish said:
1 decade ago
Towel is like rectangle, so area of rectangle is (l*b).
Let l=100, and b =50, so area =l*b =1500.
In question 20% decrease in length and and 10% decrease in breadth.
So new length is 80 and new breadth is 45, so new area =80*45 = 3600.
% decrease in area is (A1-A2) /A1*100 = 28%.
Let l=100, and b =50, so area =l*b =1500.
In question 20% decrease in length and and 10% decrease in breadth.
So new length is 80 and new breadth is 45, so new area =80*45 = 3600.
% decrease in area is (A1-A2) /A1*100 = 28%.
Sania said:
1 decade ago
But shouldn't the area of a towel be (l+b).
Rahul said:
1 decade ago
If Area, A=XY
the d(A)/A= dX/X + dY/Y
=10+20
=30%
Whats wrong with this method of differentiation?
because answer is not matching.
the d(A)/A= dX/X + dY/Y
=10+20
=30%
Whats wrong with this method of differentiation?
because answer is not matching.
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