A bakery uses 45 pounds of flour to bake 300 muffins. Assuming the same ratio, how many pounds of flour are needed to bake 20 muffins?
For ratio questions like this, quickly convert the given ratio into a unit rate ("per 1"), then multiply to reach the desired quantity. Specifically, take the total amount divided by the total items to get the amount per item, and then multiply by the new number of items. Alternatively, you can set up a proportion, , and solve for using cross-multiplication. Always check that your answer is reasonable: if the new number of items is smaller than the original, the new amount should be proportionally smaller too.
Hints
Think in terms of "per muffin"
Try to find how many pounds of flour are used for just 1 muffin by using the information about 45 pounds for 300 muffins.
Use division to get the unit rate
Divide 45 by 300 to find the number of pounds per muffin, or simplify the fraction .
Scale up from 1 muffin to 20 muffins
Once you know how many pounds are used for 1 muffin, multiply that amount by 20 to get the total flour for 20 muffins.
Desmos Guide
Use Desmos to compute the proportional amount
In the Desmos expression line, type 45/300*20 and look at the numeric result; that value is the number of pounds of flour needed for 20 muffins at the same rate.
Step-by-step Explanation
Write the ratio as a unit rate
We know the bakery uses 45 pounds of flour for 300 muffins. To find how many pounds are used for 1 muffin, divide:
Simplify this fraction to get the unit rate (pounds of flour for 1 muffin).
Simplify the fraction
Simplify by dividing numerator and denominator by 15:
So the bakery uses of a pound of flour for each muffin.
Scale the unit rate up to 20 muffins
Now multiply the flour per muffin by 20 muffins:
The 20s cancel, leaving pounds of flour, so the correct answer is B) 3.