### Discussion :: Area - General Questions (Q.No.7)

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%. |

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