Question

Difficulty: MediumSystems of Linear Equations

A boutique bookstore sells hardcover books for $25\$25 each and paperback books for $12\$12 each. On a certain day, the store sold a total of 8585 books and generated a total revenue of $1,579\$1,579. How many hardcover books were sold on that day?

Answer: 43 hardcover books

Answer

The total number of hardcover books sold on that day is 43.
By setting up the two linear equations h+p=85h + p = 85 (quantity) and 25h+12p=157925h + 12p = 1579 (revenue), eliminating pp yields 13h=55913h = 559, which gives h=43h = 43.

Step-by-Step Solution

1
Define variables and construct the system of linear equations
Let hh be the number of hardcover books and pp be the number of paperback books. The equations are h+p=85h + p = 85 and 25h+12p=157925h + 12p = 1579.
The total quantity of items sold gives a sum equation, and the individual prices multiplied by their quantities yield the total revenue equation.
2
Use substitution or elimination to solve for hh
Multiplying the total books equation by 12 yields 12h+12p=102012h + 12p = 1020. Subtracting this from 25h+12p=157925h + 12p = 1579 gives 13h=55913h = 559.
Eliminating pp directly isolates the variable hh representing hardcover books.
3
Calculate the value of hh
h=55913=43h = \frac{559}{13} = 43.
Dividing the remaining total revenue by the coefficient of hh yields the precise quantity.

Key Concept

Solving two-variable systems of linear equations using elimination or substitution
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