CAT 2018 Slot 2QA Question 18

Basics of QuadrilateralsEasy

The area of a rectangle and the square of its perimeter are in the ratio 1 ∶ 25. Then the lengths of the shorter and longer sides of the rectangle are in the ratio ?

Answer & solution

Correct answer: 1 : 4

  • A

    1 : 3

  • B

    2 : 9

  • 1 : 4

  • D

    3 : 8

Solution

Easy

Write area and the squared perimeter in terms of the sides ll and bb, form the ratio, and reduce it to a single equation in the ratio l:bl:b. Solve the resulting quadratic.

1

Set up the ratio. Area =lb=lb, perimeter =2(l+b)=2(l+b), so its square is 4(l+b)24(l+b)^2.

lb[2(l+b)]2=125 25lb=4(l+b)2\begin{aligned} &\frac{lb}{\big[2(l+b)\big]^2}=\frac{1}{25}\\ &\Rightarrow\ 25\,lb=4(l+b)^2 \end{aligned}
2

Introduce the side ratio. Let t=lbt=\dfrac{l}{b} and divide through by b2b^2.

25t=4(t+1)2 4t2+8t+425t=0 4t217t+4=0\begin{aligned} &25t=4(t+1)^2\\ &\Rightarrow\ 4t^2+8t+4-25t=0\\ &\Rightarrow\ 4t^2-17t+4=0 \end{aligned}
3

Solve the quadratic.

t=17±289648=17±158 t=4ort=14\begin{aligned} &t=\frac{17\pm\sqrt{289-64}}{8}=\frac{17\pm 15}{8}\\ &\Rightarrow\ t=4\quad\text{or}\quad t=\frac14 \end{aligned}

So the longer-to-shorter ratio is 44, i.e. shorter : longer =1:4=1:4.

shorter:longer=1:4\text{shorter}:\text{longer}=1:4

Related Basics of Quadrilaterals questions

See all Quadrilaterals & Polygons questions →
CAT 2018 Slot 2 QA Q18: The area of a rectangle and the square of its perimeter are in the ratio 1 ∶ 25. Then the lengths of the short — Solution | TheCATExam