Measurement and Data
This domain covers telling time, measuring and estimating length, reading scaled graphs, and understanding area and perimeter. Grade 3 measurement connects directly to multiplication: area is the number of unit squares that cover a shape.
Core rules
- Tell time to the nearest minute; elapsed time is the difference between start and end.
- A scaled bar graph must be read with its key or scale; one square might stand for 5 votes.
- Area of a rectangle = length × width; perimeter is the distance around the outside.
- Area is measured in square units; perimeter is measured in linear units.
Worked example
A rectangle is 5 cm long and 3 cm wide. Find its area and perimeter. Area: 5 × 3 = 15 square centimeters, because the rectangle holds 15 unit squares. Perimeter: 5 + 3 + 5 + 3 = 16 centimeters. Elapsed time: a movie starts at 2:45 and ends at 3:20. From 2:45 to 3:00 is 15 minutes; from 3:00 to 3:20 is 20 minutes; the total is 35 minutes.
Traps that cost marks
- Swapping area and perimeter, or labeling area with cm instead of sq cm.
- Reading the top of a bar against the wrong scale line.
- Subtracting 45 from 20 in elapsed-time problems and getting a negative number; bridge across the hour instead.
- Estimating a pencil as 15 meters rather than 15 centimeters.