A constant rate in pounds per hour means the same amount of flour is used each hour. Subtract the target amount remaining from the starting amount to find the amount used. Then set rate times hours equal to that amount and solve with a Desmos regression. Don’t mistake pounds used for hours elapsed.
Hints
- Hint 1
The amount left and the amount used are different. Subtract what the bakery wants to have left from what it started with. How many pounds must the bakers use?
- Hint 2
A rate of pounds per hour tells you how much flour is used in one hour. Multiply it by the unknown number of hours to get total pounds used. What should that total equal?
- Hint 3
A Desmos regression can find the unknown hours. Write the hours as and replace the equals sign with . The value Desmos reports will be a time, not an amount of flour.
Step-by-step
Find the flour used, then solve for time
Step 1Find how much flour must be used
The bakery starts with pounds and wants 1 pound remaining, so the amount used is the difference. Subtract the amount left from the starting amount: . The bakers must use pounds, not spend 9 hours.
- Step 2
Match the hourly use to the total used
Let be the number of hours. At the given rate of pound per hour, the bakers use pounds in hours. Set that equal to the 9 pounds they must use:
- Step 3
Solve for the hours in Desmos
Type in Desmos. The subscript in and the tell Desmos to find the unknown value rather than make a slider. Under PARAMETERS, it shows . So 12 hours pass before only 1 pound remains. Choice C.