## Unofficialllyy one year ago I need help with this geometry question. I will fan and medal.

1. 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.

2. 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?

3. Unofficialllyy

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

4. Unofficialllyy

@Loser66 ?

5. Loser66

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

6. Unofficialllyy

Or divide by 4? I dont know

7. Loser66

$$\div 4$$

8. 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.

9. Loser66

ha!! |dw:1437249945106:dw|

10. Unofficialllyy

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

11. 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

12. Unofficialllyy

Yeah but I need help with solving for the volume

13. Loser66

why? just replace r = 70 and you got it

14. Unofficialllyy

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

15. Loser66

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

16. Unofficialllyy

So then I do 70^3 first right?

17. Loser66

put it into calculator, then divide the answer by 4

18. Unofficialllyy

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

19. anonymous

yeah do 70^3 first

20. Loser66

ok!!

21. Unofficialllyy

Then I multiply pi and 343000?

22. 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

23. Unofficialllyy

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

24. Unofficialllyy

I mean 4/3

25. anonymous

yep thats right

26. Unofficialllyy

Then what?

27. anonymous

You can multiply it by either pi or 4/3

28. Unofficialllyy

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

29. anonymous

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

30. Unofficialllyy

In decimal form thats 1436755.04024173

31. Unofficialllyy

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

32. anonymous

yep

33. Unofficialllyy

359188.76006043

34. Unofficialllyy

And it has to be rounded to the nearest whole number

35. anonymous

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

36. Unofficialllyy

Yes it is above

37. anonymous

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

38. anonymous

Thats how I remember weather to round up or down

39. Unofficialllyy

so it would be 359189?

40. anonymous

yep

41. Unofficialllyy

Thank you so much!!

42. anonymous

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

43. Unofficialllyy

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

44. Loser66

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