Posted by **mary** on Monday, April 18, 2011 at 12:37pm.

find the surface area of a right cylinder with a diameter of 4cm and a height of 6cm. Round to the nearest hundredth.

Book answer is 100.53cm^2 I came up with 150.79cm^2

my work:

2rr(4)6)=150.79cm^2 What did I do wrong??

- Geometry -
**MathMate**, Monday, April 18, 2011 at 1:34pm
The book answer is correct.

There are two things you need to watch for:

1. The diameter is 4 cm means the radius is 2 cm.

For the formula 2πrh, you have substituted 4 for the radius, which therefore gave twice the value it is supposed to have, namely 75.40 sq.cm.

2. The other 25.13 comes from the area of the two ends, each given by πr². (Note: r=2 cm).

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