ACT Chemistry Calculations and Conversions

Finding Y from X

1. Locate the X value on the horizontal axis
2. Draw a vertical line up to the curve/line
3. Draw a horizontal line to the Y axis
4. Read the Y value

Finding X from Y

Reverse the process: start at Y, go to the curve, then down to X.

$\text{Average} = \frac{\text{sum of values}}{\text{number of values}}$

Used when asked for the mean of repeated trials.

$\text{Rate} = \frac{\text{change in quantity}}{\text{change in time}}$

Example: If 40 mL of gas is produced in 20 seconds: $\text{Rate} = \frac{40}{20} = 2 \text{ mL/s}$

$\text{Percentage} = \frac{\text{part}}{\text{whole}} \times 100$

$\text{Percentage change} = \frac{\text{new} - \text{old}}{\text{old}} \times 100$

• Direct proportion: if X doubles, Y doubles (y = kx)
• Inverse proportion: if X doubles, Y halves (y = k/x)
• On the ACT, look for these patterns in data tables

• Interpolation: estimating a value BETWEEN known data points
• Extrapolation: estimating BEYOND the range of data (less reliable)
• Use the trend line to make estimates

• Calculations on ACT Science are simple — no calculator needed
• Estimate when possible; exact answers aren't always required
• Watch for unit mismatches between answer choices
• Use the answer choices to guide your calculation accuracy
• Round intermediate values to keep things simple