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

i did it myself and i got 4.2 (b) hope its right

step-by-step explanation:

-362

step-by-step explanation:

(12)(4)+2(12)-34(12)+2(12)-3

  \/         \/         \/         \/

  48 +   24 -   408 + 24 - 3

      \   /               \   /

          72     -     432 - 3 = -363