Answer:
The chemistry class mixed 120 gallons of 12% isopropyl alcohol and 180 gallons of 42% isopropyl alcohol.
Step-by-step explanation:
1. Let's review the information given to us to answer the question correctly:
Amount of isopropyl alcohol made by the chemistry class = 300 of 30%
Amount of 12% isopropyl alcohol mixed by the chemistry class = x
Amount of 42% isopropyl alcohol mixed by the chemistry class = 300 - x
2. How much of each did they use?
Let's write our equation to solve for x, this way:
30% = 0.3, 12% = 0.12, 42% = 0.42
0.12x + 0.42 (300 - x) = 0.3 * 300
0.12x + 126 - 0.42x = 90
-0.3x = 90 - 126
-0.3x = -36
x = -36/-0.3
x = 120 ⇒ 300 - x = 180
Let's prove x = 120 is correct
0.12x + 0.42 (300 - x) = 0.3 * 300
0.12 * 120 + 0.42 (300 - 120) = 0.3 * 300
14.4 + 75.6 = 90
90 = 90
We proved x = 120 is correct
