Subscribe

9th grade · Math · Unit 21 of 22

Units & Accuracy

Let the units guide you

What your child practices

Using units to set up and check multi-step problems (gallons per minute times minutes), choosing sensible scales for graphs, and reporting answers to an accuracy that fits the measurements.

New York State Learning Standards learning standard: AI-N.Q.1; AI-N.Q.3 · using units to guide multi-step problems, formulas and graph scales, and choosing a level of accuracy that fits the measurements

How we explain it

Children can open this short lesson before they practice.

  1. Write the units with every number; they show which numbers to multiply or divide.
  2. Units cancel like factors: (gallons/minute) × minutes = gallons.
  3. Report an answer only as accurately as the measurements allow, and money to the nearest cent.

Example: A hose sprays 4 gallons per minute. How many gallons in 2 hours? 2 hours × 60 minutes per hour = 120 minutes. 120 minutes × 4 gallons per minute = 480 gallons. Answer: 480 gallons

Units & Accuracy in New York

In the New York State Learning Standards, this is unit 21 of 22 in 9th grade Math, after Parabolas & Lines and before The Correlation Coefficient.

Gradelings describes a child's practice on this unit as Beginning, Approaching, Meeting or Exceeding (Four practice steps). That reflects practice, not a report-card mark: the teacher decides the mark.

Source: New York State Education Department (NYSED)

Sample questions

A taste of this unit. In the app, questions change every time and get easier or harder to match your child.

  1. Question 1

    $50 is shared equally by 3 people. A calculator shows 16.6666667. How should you report each share?

    • $16.66667
    • $16.7
    • $16.6666667
    • $16.67

  2. Question 2

    Coffee costs $4 per pound. There are 16 ounces in a pound. What do 64 ounces cost, in dollars?

    • 16
    • 256
    • 4
    • 64

  3. Question 3

    How many seconds are in 6 hours?

    • 360
    • 21,600
    • 3600
    • 2160

  4. Question 4

    A graph of a town's population from 1990 to 2020 starts its time axis at 1990. Why?

    • every graph must start at 1990
    • the town was founded in 1990
    • it makes the population bigger
    • the data starts in 1990, so the axis need not start at year 0

  5. Question 5

    $100 is shared equally by 6 people. A calculator shows 16.6666667. How should you report each share?

    • $16.66667
    • $16.7
    • $16.6666667
    • $16.67

  6. Question 6

    A car drives 280 miles in 4 hours. What is the rate, with units?

    • 0.014 hours per mile
    • 1120 miles per hour
    • 70 hours per mile
    • 70 miles per hour

More 9th grade