Aptitude - Area - Discussion

The rational number with recurring decimal expansion 0.12 is __________.

Can anyone answer the question?

Trick:
If increase in length of breadth & width is x% then the increase in area a' = 2x + (square x)/100.

Quick method: if x=20% then a'.

20 * 2 + (20 * 20 = 4.00) = 44.00.

If x = 4 then a' = 4 * 2 + 0.(4 * 4) = 8 + 0.16 = 8.16%
If x = 5 then a' = 5 * 2 + 0.(5 * 5) = 10 + 0.25 = 10.25.
If x = 6 then a' = 6 * 2 + 0.(6 * 6) = 12 + 0.36 = 12.36.
If x = 7 then a' = 7 * 2 + 0.(7 * 7) = 14 + 0.49 = 14.49.
If x = 8 then a' = 8 * 2 + 0.(8 * 8) = 16 + 0.64 = 16.64.
If x = 9 then a' = 9 * 2 + 0.(9 * 9) = 18 + 0.81 = 18.81.
If x = 10 then a' = 10 * 2 + 0.(10 * 10) = 20 + 1.00 = 21.
If x = 11 then a' = 11 * 2 + 0.(11 * 11) = 22 + 1.21 = 23.21.

Note : When the product is a number of more than three decimals, place a decimal point after two places from the right.

What if you don't know what the percentage of increase or decrease is and what if one side is increasing and the other is decreasing?

Let a = percentage change(increase or decrease)on one side and b= percentage change of other side then:
If both sides as are increasing = (a + b) + ab/100.
If both sides are decreasing = (a + b) - ab/100.
If one side is increasing (positive, say a) and one side is decreasing (negative, say b) = a - b - ab/100.

Why all of them taking a length as 100 that and is not a square. Why don't you try it length and breadth with separate values like 100 & 200?

Let original length and breadth be 100.
So new length and breadth are 120
New Area = 120 * 120 so 14400.
Old area = 100 * 100 = 10000.
So diff = 4400.
Error = 4400/(100 * 100) * 100.
So, 44%.

Assume that total area is 100.

20% of 100 = 120.

20% of 120 = 144.

144 - 100 = 44.

Make it simple yar! Parentage increase increase of rectangle or square will be same.

Assume 10 x 10 original square Area will be 100 simple.

Now increase side length by 20 % will make 12 x 12 square Area will be 144.

So simple should I tell you the correct answer (C) 44.

Given sides of rectangle are increased by 20%.

Let us take length L = 20.

Breadth B = 10.

Area of rectangle = LxB = 10x20 = 200.

After 20% increase L = 24.

B = 12.

Area of rectangle = LxB = 24x12 = 288.

Area increased to 288 from 200 = 44%.

Same for square.

I can't understand your answer. Please explain brief.

Old a b ==> ab.

New 1.2 a 1.2 b ==> 1.44 ab.

Increase = 1.44 ab - ab = 0.44 = 44%.