Adele went to the post office to buy stamps and postcards. She bought a total of 25 stamps, some 39-cent stamps and the rest 23-cent postcards. If she paid $8.47 altogether, how many 39-cent stamps did she buy?
2 Answers
She bough 17 39-cent stamps and 8 23-cent postcards.
Explanation:
It is sometimes easier when dealing with problems like this to convert the money amount into cents, to avoid working with decimals. $8.47 equals 847 cents, which is what we can use for this problem.
Let's assume the following variables for the problem:
Since we're told that 25 items (stamps?) were bought in total, we get the following equation:
We also know that 847 cents was spent altogether. If there were
We have two variables, but two equations, so we have everything we need to finish the problem. In equation [A] we can solve for
We can now substitute this expression for
She bough 17 39-cent stamps and 8 23-cent postcards.
Adele bought
Explanation:
This is a system of equations question. Let's first define our variables.
Let
We know that the total number of stamps is
We also know the total cost of the stamps is
Since we have
Now that we have two equations, we can simply solve.
First, I'll multiply the second equation by
Next, I'll multiply the first equation by
Subtracting the second equation from the first equation, we get:
Thus, Adele bought