# ACT Math 4.1 Plane Geometry

ACT Math: Plane Geometry Drill 4, Problem 1. What is the radius of the sphere?

 ACT Math Plane Geometry ACT Mathematics Plane Geometry Foreign Language Arabic SubtitledChinese SubtitledKorean SubtitledSpanish Subtitled Geometry 3D Geometry Language English Language Plane Geometry Applications of geometry to three dimensionsSimple 3D geometryVolume Product Type ACT Math

### Transcript

00:18

is the radius from the center of the Earth to the crispy crust.

00:22

That's R. That formula: four-thirds times quantity pi R cubed.

00:27

We just need to solve for R. So for starters...

00:30

multiply both sides by three-fourths and we have pi R cubed

00:33

equals three-fourths times 288 pi. Rewrite the equation

00:38

as pi R cubed equals 216 pi

00:41

and we can get rid of the pi on both sides by dividing it out and we're left

00:45

with R equals the cube root of 216.

00:49

So the answer is 6 and yeah, 216 is a way out their number

00:55

so you can just started by multiplying out three times three to get nine times

01:00

three with just 27. Too low. Then try four

01:03

and five and you have found your way to six pretty quick.

01:06