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ACT Mathematics Videos 164 videos
ACT Math: Coordinate Geometry Drill 1, Problem 1. Which inequality is expressed by the number line?
ACT Math: Intermediate Algebra: Drill 3, Problem 1. Find the fifth number in the series.
ACT Math: Pre-Algebra Drill 1.2. What proportion of Jenna's day is spent Wii-swimming?
ACT Math 4.1 Plane Geometry 1147 Views
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ACT Math: Plane Geometry Drill 4, Problem 1. What is the radius of the sphere?
Transcript
- 00:02
For a good time solve this shmoopy question...
- 00:04
A sphere has a volume of 288pi inches cubed.
- 00:09
What is the radius of the sphere?
- 00:11
And here are your options...
- 00:17
Alright, the key thing we have to know...
Full 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
Anyway, the answer is R equals 6 or answer C.
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