# Aptitude - Area - Discussion

### Discussion :: 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:

 [A]. 10% [B]. 10.08% [C]. 20% [D]. 28%

Explanation:

Let original length = x and original breadth = y.

Decrease in area
 = xy - 80 x x 90 y 100 100
 = xy - 18 xy 25
 = 7 xy. 25 Decrease % = 7 xy x 1 x 100 % = 28%. 25 xy

 Santho said: (Jul 19, 2011) x+y-(x*y/100) Then, 20% + 10%-[20*10/100] = 28%

 Nani said: (Aug 16, 2011) Please explain clearly anyone of you.

 Xyz said: (Sep 8, 2011) SANTHO your explanation short and sweet. But why we use x+y in all problems your formula will work or not?

 Sabir said: (Dec 12, 2011) Nanii .. Let the original length be 100cm n d breadth be also 100 cm the lengths n breadths after washing will be 80 and 90 .. Original area= 100*100 = 10000 cm2 New Area= 80*90 = 7200 cm2 So percentage decrease = (10000-7200)/100 = 2800/100 = 28% :)

 Ajay said: (Jul 26, 2012) Let the original length be 20, and breadth = 10. Therefore original area = 200. After decrease, 20 reduced to 16 (20% reduction in length). 10 reduced to 9 (10% reduction in breadth). Therefore 16 x 9 = 144. 200 - 144 = 56. 56/200 = 0.28 i.e. 28%.

 Zubair Khan said: (Aug 3, 2012) Let width=x and length=y Area(A1)=xy New meters after washing- Width reduced by 20% and length by 10% Thats why Width= x-x*(20/100)=x*{1-(2/10)}=x*8/10 Lenght= y-y*(10/100)=y*{1-(1/10)}=y*9/10 New area(A2)= xy*72/100 Area reduced=A1-A2 =xy{1-(72/100)} =xy*(28/100) Now it is showing clearly area reduced is 28% ans. Note= 2% of x means (x*2/100) =28% of xy means(xy*28/100)

 Abc said: (Aug 27, 2012) x+y-(x*y/100)------------when area is decreasing x+y+(x*y/100)---------------when area is increasing,all this type of prblms.

 Manoranjan said: (Sep 29, 2012) Hi. Take L=100 nd B=100. Then 20% in L and 10% in B. Then new L and B are 80 and 90. Area=100*100=10000. New area =7200 then 10000-7200=2800. Now 2800/10000*100=28 answer.

 Rahul said: (Oct 13, 2012) 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.

 Sania said: (May 15, 2013) But shouldn't the area of a towel be (l+b).

 Manish said: (Jul 27, 2013) 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%.

 Samuel said: (Aug 9, 2013) 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%.

 Harsha said: (Mar 24, 2014) A1 = 100*100 = 10000 (ORIGINAL AREA). A2 = 80*90 = 7200 (DECREASED IN AREA). A2-A1 = 2800. (A2-A1)% = 28%.

 Kunal said: (Apr 26, 2014) 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.

 Sriram said: (Dec 3, 2014) So simple by a formula. x% decrease in length y% decrease in breadth then area change is -x-y+(x*y)/100.

 Sam said: (Jul 30, 2016) x + y - (x * y/100). Then, 20% + 10% - [20 * 10/100]. 30% - 2% = 28%.

 Islam Ansari said: (Sep 4, 2016) xy - 18/25xy. = 7/25xy. How?

 Sreelu said: (Oct 26, 2016) 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.

 Dhanraj said: (Mar 19, 2017) How 7/25 came there? Explain it.

 Jatin said: (Feb 11, 2018) -20-10+20*10/100 = 28%.

 Pinku said: (Aug 27, 2019) x=a*80/100 y=b*90/100 Area=x*y=80*a*90*b/100*100=72/100(a*b) decreased area=total area(ab)-72ab/100 =ab-72ab/100 =100-72(ab/100) =28/100(ab) = 0 .28ab or 28ab%. Decreased area by 28%.