Unchanged Rectangle

Algebra Level 3

If the length of a rectangle is increased by 150 % 150\% , its width is decreased by w % w\% and its area remains unchanged, what is the value of w w ?



The answer is 60.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

3 solutions

Let the original length and width of the rectangle be L 1 L_1 and W 1 W_1 respectively and its area A A . Then A = L 1 W 1 A = L_1W_1 . Let the increased length be L 2 L_2 and the decreased width be W 2 W_2 . Then A = L 2 W 2 A=L_2W_2 and

L 2 W 2 = L 1 W 1 ( 1 + 150 100 ) L 1 ( 1 w 100 ) W 1 = L 1 W 1 5 2 ( 1 w 100 ) = 1 1 w 100 = 2 5 w 100 = 1 2 5 = 3 5 w = 3 5 × 100 = 60 \begin{aligned} L_2 W_2 & = L_1 W_1 \\ \left(1+ \frac {150}{100} \right)L_1 \left(1-\frac w{100} \right) W_1 & = L_1 W_1 \\ \frac 52 \left(1-\frac w{100} \right) & = 1 \\ 1 - \frac w{100} & = \frac 25 \\ \frac w{100} & = 1 - \frac 25 = \frac 35 \\ \implies w & = \frac 35 \times 100 = \boxed{60} \end{aligned}

Nice explanation!

Brendon Teong - 10 months, 1 week ago

Log in to reply

Glad that you like it.

Chew-Seong Cheong - 10 months, 1 week ago

Let the initial values of length and breadth of the rectangle be l l and b b , then

l b = l ( 1 + 150 100 ) b ( 1 w 100 ) lb=l\left (1+\dfrac {150}{100}\right )b \left (1-\dfrac {w}{100}\right )

w = 100 ( 1 2 5 ) = 60 \implies w=100\left (1-\dfrac 25\right )=\boxed {60} .

Brendon Teong
Aug 7, 2020

If z w % = 2 z-w\%=2 , then x = 1 x=1 .

100 + 150 = 250 100+150=250

250 × 2 = 500 250 \times 2=500

100 × 5 = 500 100 \times 5= 500

100 % 2 5 = 60 % 100\% - \frac {2} {5}=60\%

w = 60 w=\boxed{60}

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...