Time is not base ten

What this lesson shows

Fixes a mistake

9:55 to 10:05 is 10 minutes, not 50. An hour has 60 minutes.

The worked example

The lesson works this one step by step: 9:55 a.m. to 10:05 a.m. Then your kid tries one like it on paper.

The steps

1. An hour is 60 minutes
2. Count up to the hour
3. Then past it
4. Add the two

Helping at home

An hour has 60 minutes, not 100, so subtracting clock times like whole numbers goes wrong across an hour. Count up instead: minutes to the next whole hour, then the minutes after it, and add the two.

If your kid gets stuck

Count up to the next whole hour first.

Standards

• Common Core 4.MD.A.2
  Use the four operations to solve word problems involving distances, intervals of time, liquid volumes, masses of objects, and money, including problems involving simple fractions or decimals, and problems that require expressing measurements given in a larger unit in terms of a smaller unit. Represent measurement quantities using diagrams such as number line diagrams that feature a measurement scale.

More in this unit

• Measuring to the nearest eighth inch
• Converting units with a table
• Multiply or divide?
• Elapsed time on a number line
• Time zones
• Does that measurement make sense?