## anonymous one year ago for this question do you divide?

1. anonymous

A weather balloon holds 2,850 cubic meters of helium. The density of helium is 0.1685 kilograms per cubic meter. How many kilograms of helium does the balloon contain? Please round your answer to the nearest whole number. Only enter a numerical value in the answer blank.

2. anonymous

you would divide 2850 / 0.1685?

3. jim_thompson5910

If you knew the mass and volume, you divide to get the density. However, we don't know the mass which is why we end up multiplying instead (think of it as undoing division) Density = mass/volume D = m/v 0.1685 = m/2850 0.1685*2850 = m ... Multiply both sides by 2850 to isolate m m = ??.

4. anonymous

i got 480.225

5. anonymous

is that correct?

6. anonymous

@jim_thompson5910

7. jim_thompson5910

I'm getting the same. Then you round to the nearest whole number.

8. anonymous

so 480

9. anonymous

can you check one more question?

10. jim_thompson5910

sure

11. anonymous

The population of Tinyville is 16.2 Tinys per acre. Exactly 405 Tinys live in Tinyville. How many acres is Tinyville? Only enter a numerical value in the answer blank.

12. anonymous

i got 0.04

13. anonymous

should i have multiplied?

14. jim_thompson5910

population density = (# of people total)/(total area)

15. jim_thompson5910

population density = 16.2 Tinys per acre # of people total = 405 tinys area = unknown

16. jim_thompson5910

let x = unknown area population density = (# of people total)/(total area) 16.2 = 405/x x = ??

17. anonymous

i got 25 0.0

18. jim_thompson5910

25 acres is correct

19. jim_thompson5910

hopefully that's a face after the 25? and it's not two hundred fifty point zero?

20. anonymous

yeah its a face lol

21. jim_thompson5910

I thought so but wasn't sure lol

22. phi

one way to keep things straight about multiplying or dividing is to use ratios when you see "16.2 Tinys per acre" read 16.2 Tinys per 1 acre" and the word "per" read as "divided by" that is, write the ratio $\frac{ 16.2 \ Tiny }{1 \ acre}$ Next they say: Exactly 405 Tinys ... x (unknown acres) write another ratio of # of Tiny's divided by number of acres $\frac{ 16.2 \ Tiny }{1 \ acre} = \frac{405}{x}$ now you "solve for x"

23. phi

the first trick, is if the x is in the bottom, you can "flip" both sides $\frac{1 \ acre} { 16.2 \ Tiny }= \frac{x}{405 \ Tinys}$ now to "solve for x" multiply both sides by 450 Tinys $\frac{1 \ acre} { 16.2 \ Tiny } \cdot 450 \ Tinys= \frac{x}{405 \ Tinys} \cdot 450 \ Tinys$ and that simplifies to $\frac{ 450}{16.2} \ acres= x$