NEED HELP PLEASE

Mixture Problems
1.Joe created a metal containing 40% platinum by combining two other metals. One of these other metals weighed 12 lb. and contained 45% platinum. If the other weighed 3 lb. then what percent of it was platinum?
2. 12 gal. of a saline solution was mixed with 3 gal. of a 30% saline solution to make a 38% saline solution. Find the percent concentration of the first solution.
3. 9 ml of a 20% alcohol was mixed with 6 ml of pure water. Find the concentration of the new mixture.
4. How much clay do you need to add to 8m^3 of soil with 30% clay in order to make a soil with 60%?
5. 9 L of an alcohol solution was mixed with 1L of a 80% alcohol solution. Find the percent concentration of the first solution.

1 answer

1)

The final mixture weighs 12 + 3 = 15 pounds and is 40% platinum.

Thus you need .40 x 15 = 6 pounds of platinum total from the two metals that were combined.

The first metal contained .45 x 12 = 5.4 pounds of platinum.

The second metal must then contain 6 – 5.4 = 0.6 pounds of platinum.

You know the second metal weighs 3 pounds.

You need to determine what percent 0.6 is of 3.

The second metal is then 0.6 / 3 = 0.2 or 20% platinum.