Draw and use a double number line diagram to model and solve the problem below.
Leah gets to paint her room since she bought a new bedspread set. Two gallons of paint covers 800 square feet. How many gallons of paint will Leah need to paint her entire room, which is 1,200 square feet?
Let's draw a double number line to represent the problem. On the top line, we will put gallons of paint, and on the bottom line, we will put the square footage of the room.
[Image: A double number line where the top line represents gallons of paint and the bottom line represents the square footage of the room. The top line has 1 and 2 above the line and arrows pointing to 1 and 2 on the line. The bottom line has 400 and 800 below the line and arrows pointing to 400 and 800 on the line.]
According to the given information, two gallons of paint are enough for 800 square feet. Let's also mark one gallon on our number line corresponding to 400 square feet (half of 800 square feet).
[Image: The double number line now has an additional mark that one gallon corresponds to 400 square feet.]
Leah's room is 1,200 square feet, which is 400 square feet more than 800 square feet. Since one gallon of paint covers 400 square feet, she will need an additional gallon of paint to cover the entire room.
Thus, Leah will need a total of 3 gallons of paint to cover her 1,200 square foot room.