Question

A cone has a base radius of 7 centimeters and a height of 21 centimeters.

What is the volume of the cone?

A.
28π cm3

B.
49π cm3

C.
147π cm3

D.
343π cm3


@undeadknight26

Answer 1

i think its A

Answer 2

i got 2 formulas...would u know which one was correct? i got:
1/3 × pi × r^2 × h
and
1/3 × b × h

Answer 3

either formula i use i get a weird answer...with the first formula(1/3 × pi × r^2 × h)i got 609 and with the second formula i got 48.5...

Answer 4

it would be B then

Answer 5

Generally figures which come to a single point (the tip of a cone, or a pyramid) have 1/3 the area of their prism counterpart.

Both formulas are correctly written as: 1/3 x Area of base x height But a cone has a circular base, so
volume = 1/3 x (pi r^2) x height

Answer 6

radius is 7, and height was 21: Plug it all in:
1/3 * pi (7)^2 * 21
And leave pi as it is. :)

Answer 7

how do i do the ^ part :o

Answer 8

7^2 is an exponent
exponent just means repeated multiplying.
So 7^2 means multiply 7 two times, or 7 times 7.

Answer 9

Similarly 3^3 would mean multiply 3 three times, or 3 * 3 * 3. Does that make sense?

Answer 10

yes

Answer 11

So:
1/3 * pi 7^2 * 21
1/3 * 7 * 7 * 21 * pi <-- that pi is just going to come along for the ride now.
We could use a calculator, or notice that 21 = 7 * 3. The 3 and 1/3 multiply together to make 1, so we have:
1/3 * 7 * 7 * (3 * 7) * pi
(1/3 * 3) * 7 * 7 * 7 * pi
7 * 7 * 7 * pi

Answer 12

Its not common to have the cubed numbers memorized, so at this point we can use a calculator again: 7 * 7 * 7 = 343

Answer 13

tyhat makes alot of sense :o