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George E. Cawthon
Posts: n/a

bill wrote:

area= 3.14 x radius x radius. so the 6 inch pipe has cross section
of 100 sq inches...

We learn something new every day here...


And what we learned is that Bill gave the correct
formula and then made the simple mistake of
substituting diameter for radius and then not
thinking about what the range for the answer would
be. No criticism of Bill is intended as we all
make mistakes, but what most people don't do is
then consider if the answer makes sense.

For example, a simple 6 x6 grid of inch squares
has 36 square inches. Slap a 6" diameter pipe
down on the grid and the pipe won't cover it, so
you know the answer has to be less than 36 square
inches (no where near 100 square inches). Using
the same logic a 10" pipe wouldn't have 100 square
inches of area. By the same token a 4" pipe can't
have an area of more than 16 square inches.

Actually it is the 4" pipe is 2x2x3.14= 12.6
and 6" pipe is 3x3x3.14= 28.3

The answer is that a single 6" pipe has a larger
area than two 4" pipes.

Sorry for being pedantic, but a simple
visualization is often all that is needed to
realize an error in a mathematical problem.