Why does a 500 g jar of honey show more than 500 g on the scales? This investigation answers it with real scales. Students learn gross, net and packaging (tare) mass from a deli scale ticket, then weigh real things in groups and write up what they found.
How it runs
Three lessons of 45–60 minutes.
- Lesson 1: warm-up, key words, gross, net and packaging mass, a worked deli-ticket example, finding net mass with any scales, a packaged food table and six word problems.
- Lesson 2: two investigations with scales: the mass of the food in a lunchbox, and the mass of the items in a container. Students check their answer by weighing the items on their own.
- Lesson 3: the write-up, a cereal savings task, the case file, challenge levels and reflection.
Maths covered
- MA3-NSM-01: measure with scales, record to 3 decimal places, convert between g and kg, and solve problems with different units of mass
- MA3-AR-01: subtract to find the net mass in multistep problems
Good to know
- Works with any kitchen or classroom scales: weigh it full, weigh the empty container, subtract. TARE is shown as a shortcut, not a requirement.
- Gross and net mass go a little beyond the Stage 3 wording, so it suits a fast-finisher group or a hands-on maths week.
- Part of the Metric Mass Unit Bundle.
