The area of a rectangle remains unchanged when it is made 1cm shorter and 1cm wider or when it is made 8cm longer and 4cm narrower. Its area, in square cm

Answer 1

Let's say the rectangle is x by y
A = xy =(x-1)(y+1) = (x+8)(y-4) which give x=10 & y=9 and so its area 90 sq cm.