Question 327367
If 5 machines produce 12 gallons in 10 days, then it would take 5 machines to produce 24 gallons in 20 days, 36 gallons in 30 days, 48 gallons in 40 days.

It takes 5 machines 40 days to produce 48 gallons, so intuituvely, we know 4 machines will take longer.

40/(4/5)=50 days for 4 machines to produce 48 gallons.

Another way to look at it is noting that if 5 machines produce 12 gallons in 10 days, then each machine produces .24 gallons per day. See, if 5 machines produce 12 gallon in 10 days, then 5 machines produce 1.2 gallons per day.
1.2/5=.24

Now, since each machine produces .24 gallons per day, 4 machines produce

.96 gallons per day. 48/.96=50 days.