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Exercises Numbers, fractions and percents

Example 5.38 from Prealgebra, 5.3 Decimals and Fractions

Decimals and Fractions: example 5.38

A circle has radius $42.5$ centimeters. Approximate its ⓐ circumference and ⓑ area.

Work it out on paper first. Then open the solution one step at a time, and stop as soon as you can finish on your own.

Solution

ⓐ Find the circumference when $r = 42.5 .$

Write the formula for circumference. $C = 2 π r$

Substitute 3.14 for $π$ and 42.5 for $r$ $C \approx 2 (3.14) (42.5)$

Multiply. $C \approx 266.9 centimeters$

ⓑ Find the area when $r = 42.5$ .

Write the formula for area. $A = π r^{2}$

Substitute 3.14 for $π$ and 42.5 for $r$ . $A \approx (3.14) {(42.5)}^{2}$

Multiply. $A \approx 5671.625 square centimeters$

Your turn

The book's Try It right after this example: same idea, new numbers. Only the answer is given.

A circle has radius $51.8$ centimeters. Approximate its ⓐ circumference and ⓑ area.

How did it go?

PreviousDecimals and Fractions: example 5.37 Next Decimals and Fractions: example 5.39

From Prealgebra (1st edition) by OpenStax (Rice University), section 5.3, licensed under CC BY 4.0. Original at openstax.org. We split the solution into steps; the words, numbers and figures are the book's. OpenStax doesn't endorse this site.