Gold Coin Weight Grams

By admin, on May 24th, 2010

Word Problem help please?!!?

3 different questions- may have to go to add details….show work….
1) How many liters of water should be evaporated from 160L of a 12% saline solution so that the solution that remains is 20% saline.
2)A bag contains 42 coins w/ a total weight of 246grams. If the bag contains only gold coins at 8 grams each and silver coins @ 5 grams each. HOw many gold and how many silver coins are in the bag?
3)HOw much pure gold should be melted with 15 grams of 14-karat gold to produce 18-karat gold?
Thanks so much!! Please show work.

1) How many liters of water should be evaporated from 160L of a 12% saline solution so that the solution that remains is 20% saline.

(.12 * 160 = 19.2) x 5 = 96
160 – 96 = 64 to be evaporated

or 12/20 = .6
want to have .6 as much
.6 * 160 = 96
same result

2)A bag contains 42 coins w/ a total weight of 246grams. If the bag contains only gold coins at 8 grams each and silver coins @ 5 grams each. HOw many gold and how many silver coins are in the bag?

8g + 5s = 246
g + s = 42
5g + 5s = 210
3g = 36
g = 12
s = 30

3)HOw much pure gold should be melted with 15 grams of 14-karat gold to produce 18-karat gold?

I think pure gold is 24K
so 15K = 5/8 and 18K = 3/4

15 * 5/8 + g = 3/4 (15 + g)
75/8 + g = 45/4 + 3g/4
g/4 = 45/4 – 75/8
g = 45 – 75/2
g = 45 – 37.5 = 7.5

75/8 + 7.5 = 16.875
3/4 (22.5) = 16.875
.