Answer:
36290 min = 604.8 hr.
Step-by-step explanation:
1 lbs = 453.59237 grams.
∴ 2 lbs = 907.18474 grams.
Using cross multiplication:
500 mg of iron oxide dissolved → 20 minutes.
907184.74 mg of iron oxide dissolved → ??? minutes.
∴ The time needed to dissolve 2 lbs of iron oxide = (907184.74 mg)(20 min)/(500 mg) = 36290 min = 604.8 hr.