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Video: Finding the Circumference of a Circle given Its Diameter

Kathryn Kingham

Find the circumference of a circular pizza with a diameter of 33 inches. Round to the nearest tenth

01:60

Video Transcript

Find the circumference of a circular pizza with a diameter of 33 inches. Round to the nearest tenth.

We’re looking for the circumference of this pizza β€” the distance all the way around. We find circumference by multiplying πœ‹ times the diameter or by multiplying two times πœ‹ times the radius. In this problem, they told us the diameter was 33 inches. So let’s use πœ‹ times the diameter to solve for circumference.

Circumference equals πœ‹ times the diameter. The diameter of this pizza is 33 inches. I use my calculator to multiply πœ‹ times 33 inches. My calculator gives me 103.6725, and it continues on and on. But this question has asked us to round to the nearest tenth. There is a six currently in the tenth position. And we will look at the number to the right of the tenth to see should we round up or keep this number the same.

If the number to the right of our tenth place is between zero and four, we do not round up. If that value is between five and nine, we will round up. Seven is greater than five, which means we need to round our tenth place up. The circumference of this pizza is 103.7 inches, and that is quite a large pizza.