Question 133·Easy·Linear Equations in One Variable
A wildlife rescue cared for a total of 32 animals that were either birds or mammals. If 19 of the animals were birds, how many were mammals?
For total-and-part problems, identify the total and the known part, then either write a simple equation like or think of it as "total minus known part". On the SAT, go straight to subtraction when there are only two groups and one group plus the other equals the total.
Hints
Identify what the 32 represents
Ask yourself: does 32 represent just one type of animal, or the total number of both birds and mammals together?
Use an equation for the total
Let the number of mammals be a variable, like . Write an equation that shows birds plus mammals equals 32.
Choose the operation
If you know the total (32) and one part (19 birds), what operation do you use to find the missing part (mammals)?
Desmos Guide
Use Desmos to subtract
In the expression line, type 32 - 19 and press Enter. The value that Desmos outputs is the number of mammals.
Step-by-step Explanation
Understand the relationship
There are only two types of animals mentioned: birds and mammals. Together, they make a total of 32 animals.
So we can represent this as:
Substitute the known value
We are told that 19 of the animals are birds. Substitute 19 for "birds" in the equation:
Now we just need to solve for the number of mammals.
Solve for the number of mammals
To find the number of mammals, subtract 19 from 32:
So, the number of mammals is 13.