I need help with this geometry question. I will fan and medal.

- Unofficialllyy

I need help with this geometry question. I will fan and medal.

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- Unofficialllyy

The main tank has a radius of 70 feet. What is the volume of the quarter-sphere sized tank? Round your answer to the nearest whole number. You must explain your answer using words, and you must show all work and calculations to receive credit.

- Unofficialllyy

I know that I have to use the formula for volume of a sphere, and then once I get the volume I multiply it by 4, right?
So I have written down: \[V=\frac{ 4 }{ 3 } \Pi r^3\]
Then I plug in 70 for r: \[V=\frac{ 4 }{ 3 } \Pi(70)^3\]
Is this correct so far?

- Unofficialllyy

@welshfella could you see if you could help? :)

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## More answers

- Unofficialllyy

@Loser66 ?

- Loser66

why multiple by 4? the quarter sphere is 1/4 of the sphere. Not 4x Volume of the sphere.

- Unofficialllyy

Or divide by 4? I dont know

- Loser66

\(\div 4\)

- Unofficialllyy

But am I right so far with what I have? After I got \[V=\frac{ 3 }{ 4} \Pi (70)^3\]
I don't know how to solve this.

- Loser66

ha!! |dw:1437249945106:dw|

- Unofficialllyy

But couldn't figure out the volume first and then divide by 4?

- Loser66

Either way, you can find volume first and then take \(V\div 4\)
Or, take it directly as what I showed.
Both them give you the same answer

- Unofficialllyy

Yeah but I need help with solving for the volume

- Loser66

why? just replace r = 70 and you got it

- Unofficialllyy

I know that part. I don't know where to start though.

- Loser66

\(V =\dfrac{4}{3}\pi r^3= \dfrac{4}{3}* 3.1415* (70)^3\)

- Unofficialllyy

So then I do 70^3 first right?

- Loser66

put it into calculator, then divide the answer by 4

- Unofficialllyy

I cant just use a calculator, I have to show all calculations

- anonymous

yeah do 70^3 first

- Loser66

ok!!

- Unofficialllyy

Then I multiply pi and 343000?

- anonymous

Technically, you can do the multiplication in any order that you want (70^3 can be re written into 70*70*70) I personally find it easier to do that first

- Unofficialllyy

okay so now i have \[V=\frac{ 3 }{ 4} \Pi(343000)\]

- Unofficialllyy

I mean 4/3

- anonymous

yep thats right

- Unofficialllyy

Then what?

- anonymous

You can multiply it by either pi or 4/3

- Unofficialllyy

So if I multiply it by pi I get \[V=\frac{ 4 }{ 3 }(343000\pi)\]

- anonymous

yes. Then you would multiply that by 4/3 to get the total volume of the sphere

- Unofficialllyy

In decimal form thats 1436755.04024173

- Unofficialllyy

Then I divide that by 4 to get the volume of a quarter sphere correct?

- anonymous

yep

- Unofficialllyy

359188.76006043

- Unofficialllyy

And it has to be rounded to the nearest whole number

- anonymous

so you would take the tenths place and see if it is above or below 5

- Unofficialllyy

Yes it is above

- anonymous

5 and above, give it a shove, 4 and below leave it down low

- anonymous

Thats how I remember weather to round up or down

- Unofficialllyy

so it would be 359189?

- anonymous

yep

- Unofficialllyy

Thank you so much!!

- anonymous

No problem :) give credit to @Loser66 too. They helped out in the beginning

- Unofficialllyy

Yes they did, thank you as well @Loser66 !!

- Loser66

I am ok, I have a bunch of medals, don't care !!

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