A pharmacist needs 500 milliliters of a 20% phenobarbital solution but has only 5% and 25% phenobarbital solutions available. Find how many milliliters of each she should mix to get the desired solution.

Let x be ml of 5% soln.

let 500-x be ml of 25% soln.

.

x*.05=.05x

(500-x)*.25=125-.25x

500*.20=100

.

.05x+125-.25x=100

-.2x=-25

x=-25/-.2

x=125 ml of 5% soln.

500-x=375 ml of 25% soln.

.

Check:

125*.05= 6.25

375*.25=93.75

100

step-by-step explanation:

always plug in x. in this case, x equals 4.

i'm going to first solve 4(2+3x)

1) 4(2+3(4)) use pemdas to solve.

i'm going to multiply whats in the parenthesis first, so 3 times 4=12.

2)4 (2+12) i'm then going to multiply 4 by both numbers in the parenthesis (because multiplying comes before adding)

4 times 2= 8.   4 times 12= 48

4) (8+48)= 56 (answer)

i'm then going to solve 8+12x and plug in 4 for x.

1) 8 +12(4)

multiplying comes before adding, so i'm gonna multiply 12 and 4.

12 times 4= 48.

2) 8+48=56

both equal the same!