Grade 7 · Unit 1 · Lesson 5 · part 3 of 5
Forward and backward
The equation works in both directions.
Forward and backward
The equation works in both directions.
Know the input, want the output
c = 3.20 × 12
12 gallons cost 3.20 × 12 = $38.40. Multiply.
Know the output, want the input
48 = 3.20g
$48 buys 48 ÷ 3.20 = 15 gallons. Divide by the unit rate to undo the multiplying.
Multiply to go forward, divide to go back. That is the same unit rate doing both jobs.
Here is the slider from Lesson 4 again, now with the equation. Move r and watch the table, the line, and y = rx change together. They are three pictures of the same number.