Achemist needs 80 milliliters of a 50% solution but she only has 20% and 60% solutions available. calculate how many milliliters of each should be mixed to get the desired result. how many milliliters of the 20% solution should she use?

We have 20% and 60% solutions and need 80 ml of 50%

A) x + y = 80

B) .20x + .60y = (80 * .5)

Multiplying A) by -.2

A) -.2x -.2y = -16  Then adding this to B) we get

.4y = 24

y = 60 ml of 60%

x = 20 ml fo 20%

Source: 1728.com/mixture.htm

the answer is c: divide the arc's degree measure by 360°, then multiply by the circumference of the circle.