Question

the length of rectangle is three times its width if the perimeter is 84 cm find the length of rectangle

Answer 1

let length be x and breadth be y

then ATQ,
x = 3y

we know perimeter of rectangle = 2×(l+b)
so perimeter = 2×(x+y)

given perimeter = 84 cm

plugging in the values

2×(x+y) = 84
we know x= 3y

so putting and solving
4y = 42
y = 42/4
y = 21/2

so length is 3y
then length = 63/2 is the required answer

hope this helps.....

Answer 2

let
L be the length of the rectangle
B be the breadth of the rectangle


ACC.TO THE CONDITION
L=3B.......equation 1

perimeter of the rectangle =84

2(L+B)=84......equation 2


BY SUBSTITUTING EQUATION 1 IN EQUATION 2

2(3B+B)=84

B=42/4
=21/2........EQUATION 3


put EQUATION 3 in EQUATION 1




L=63/2
=31.5