Question

the length of rectangular field is thrice of its breadth its perimeter is 400 m what are its length and breadth ?

Answer 1

The length of rectangular field is thrice of its breadth 
let breadth be b
lenght =3b
perimeter is 400 m

perimeter of rectangle=2(l+b)
   so 400 =2(l+b)
 400=2(3b+b)  [because length is 3b]
400 =2(4b)
400=8b
b=400/8=50cm
length =3b
l =3×50
           =150 cm

length is 150m and breadth is 50m

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Answer 2

let,breadth=x m
so,length=3x m
ATQ,
2(x+3x)=400
or,x+3x=400/2
or,4x=200
or, x=200/4
therefore, x=50

hence,breadth=50 m,length=3x50m =150m.