Area of a Rectangle Outside a Rectangle

Date: 6/11/96 at 2:20:13
From: Anonymous
Subject: Area of a rectangle not in another rectangle

A rectangular swimming pool 50 m by 32 m has a concrete border
all around it.  Find the area of the concrete border if it is
2.4 m wide at the sides and 4.8 m wide at the ends.  The concrete path
is to be tiled with square tiles of side 20 cm each.  How many tiles 
will be needed?

A big group of Singaporean friends and I have been stumped over this 
question. We sincerely hope that you can help us. There seem to
be many different ways to do this question and the answers range
widely.

Yours sincerely,
Jeannette signin' off from Sunny Singapore

Date: 6/12/96 at 13:46:52
From: Doctor Darren
Subject: Re: Area of a rectangle not in another rectangle

I would approach this problem by finding the area of the rectangle 
you want _including_ the path and the pool (which has length 
50+2*4.8 = 59.6 m, and width 32+2*2.4 = 36.8 m) so the area is 
2193.28 m^2.  We then subtract the area of the pool, which is 
1600 m^2, and the area of the concrete border is 593.28 m^2.

Does this agree with any of your answers?

-Doctor Darren,  The Math Forum
 Check out our web site!  http://mathforum.org/dr.math/