Big Ideas Math: Modeling Real Life, Grade 8
BI
Big Ideas Math: Modeling Real Life, Grade 8 View details
3. Volumes of Spheres
Continue to next subchapter

Exercise 18 Page 443

The volume of a sphere is four thirds the product of π and the cube of the radius.

3.5 feet

Practice makes perfect

The volume of a sphere is four thirds the product of π and the cube of the radius. V=4/3π r^3 We want to find the radius of a sphere whose volume is 180 cubic feet. Therefore, we can substitute 180 for V in the above formula and solve it for r.

V=4/3Ï€ r^3
180=4/3Ï€ r^3
â–¼
Evaluate right-hand side
180=4 π r^3/3
3* 180 = 3 * 4 π r^3/3
3* 180 = 4 π r^3
540 = 4 π r^3
540/4π=4 π r^3/4π
540/4Ï€=4Ï€ r^3/4Ï€
540/4Ï€=r^3
sqrt(540/4Ï€)=sqrt(r^3)
sqrt(540/4Ï€)=r
r=sqrt(540/4Ï€)
r=3.502632...
r≈ 3.5

The radius of the sphere, correct to the nearest tenth, is 3.5 feet.