Computation: Applied Math with Money, Time and Measurement (CASAS Competency 6)
The Computation area tests math as adults meet it: money, percentages, measurement, time, averages, and information drawn from tables and graphs. Items are word problems and document-based tasks, so the arithmetic is rarely the hard part. Deciding what to compute is.
Core rules and concepts
- Read the question first, then pull only the numbers it needs. Extra numbers are usually supplied on purpose.
- Percent: part equals rate times whole. A discount comes off the price before tax is added.
- Money is rounded to cents, and rounding is done at the end of the calculation, not at each step.
- Time uses a 60-minute base: 1.5 hours is 90 minutes, and elapsed time across noon or midnight requires care with a.m. and p.m.
- Conversions to know: 12 inches in a foot, 3 feet in a yard, 16 ounces in a pound, 4 cups in a quart, 60 minutes in an hour.
- Average equals total divided by the number of items; to find a missing value, work backward from the total.
- Tables and graphs: check row and column headers and the unit (dollars, or thousands of dollars).
Worked example
A jacket priced at $48.00 is 15% off, and sales tax is 6%. What is the total? Reasoning: the discount is 0.15 times 48.00, or $7.20, so the sale price is $40.80. Tax is charged on the sale price: 0.06 times 40.80 is $2.448, rounded to $2.45. The total is $40.80 plus $2.45, or $43.25. Each wrong path appears among the choices: taxing the original price gives $43.68; taking 21% off the original gives $37.92 before tax; rounding early gives $43.24.
Traps that cost marks
- Adding percentages, as if 15% off plus 6% tax were 9% off.
- Charging tax on the pre-discount price.
- Mixing units (ounces with pounds, minutes with hours) before comparing.
- Estimating and then choosing a nearby choice when an exact answer is required.
- Giving the right number with the wrong unit or label.