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Determine rate of change from a table

Rate of change from a table is determined by dividing the change in the output by the corresponding change in the input, ΔyΔx\frac{\Delta y}{\Delta x}, including when input intervals are unequal. A constant ratio indicates a linear relationship and represents its slope, with positive, negative, or zero values describing the direction of change; it is not generally found by dividing yy by xx. This scope excludes instantaneous rates and formal analysis of nonlinear functions.

Detailed Explanation: Determine rate of change from a table

To find the rate of change from a table, compare how much the output yy changes to how much the input xx changes:

rate of change=ΔyΔx=change in ychange in x\text{rate of change}=\frac{\Delta y}{\Delta x} =\frac{\text{change in }y}{\text{change in }x}

Use two rows from the table.

xxyy
2277
551616
992828

Step 1: Choose two points.
Use the first two points: (2,7)(2,7) and (5,16)(5,16).

Step 2: Find each change.

Δy=167=9\Delta y=16-7=9 Δx=52=3\Delta x=5-2=3

Step 3: Divide the changes.

rate of change=ΔyΔx=93=3\text{rate of change}=\frac{\Delta y}{\Delta x} =\frac{9}{3}=3

The rate of change is 33. This means that for every increase of 11 in xx, yy increases by 33.

Check the next pair of points. The input changes by 44, and the output changes by 1212:

281695=124=3\frac{28-16}{9-5}=\frac{12}{4}=3

The rate is still 33, so the table shows a linear relationship with a slope of 33.

Do not usually divide yy by xx. Instead, divide the change in yy by the corresponding change in xx.

Learn by doing: Determine rate of change from a table

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