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Math lesson plan · 7th grade (Year 8 in England) · 60 minutes

Surface area of triangular prisms

Geometry

CCSS 7.G.B.6England: KS3 Geometry and measuresEngland: GCSE Foundation Geometry and measures

Objective and success criteria

Students will: Surface area of triangular prisms.

  • I can answer questions on today's skill on my own, without help.
  • I can explain each step and say why it works.
  • I can check my answer and spot a mistake.

Before and after

Needs first: Surface area using nets; Area of triangles

Leads to: the next skill in this area.

Materials: Rulers and protractors, Squared or dotted paper, Shape cut-outs, Mini whiteboards and pens, Printed student sheet (below).

Warm-up · 6 min

  • Quick retrieval from earlier learning (Surface area using nets; Area of triangles). Students answer on mini whiteboards.
  • Show answers together and note who needs support in the main task.
  1. What is the surface area of a cuboid 7 cm × 3 cm × 4 cm, in cm²? → 122Prompt: A cuboid has 6 faces in 3 matching pairs.
  2. A cube has edges of 3 ft. What is its total surface area, in ft²? → 54Prompt: A cube has 6 identical square faces.
  3. What is the surface area of a cuboid 5 yd × 7 yd × 7 yd, in yd²? → 238Prompt: A cuboid has 6 faces in 3 matching pairs.

Hook · 6 min

  • Show a photo of a building, a tile pattern or a road sign and ask what shapes and angles students can spot.
  • Share the objective: Surface area of triangular prisms. Read the success criteria together.

I do: model it · 12 min

  • Work through the example out loud, saying why you do each step, not just what you do.
  • Model one question from the student sheet, thinking aloud.
  • Pause after each step and ask a student to say what comes next.

We do: guided practice · 12 min

  • Do these together. Students try each step on whiteboards before you reveal it.
  • Use the hints as prompts rather than giving the answer.

You do: independent practice · 17 min

  • Students work on the student sheet. Circulate and check the first two answers of every student early.
  • Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

Exit ticket · 7 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

Watch out for

  • Thinking a square turned on its corner is no longer a square.
  • Reading the wrong scale on a protractor.

Support and stretch

Support

  • Review first: Surface area using nets.
  • Use concrete materials: rulers and protractors.
  • Give the first step of each question, or a partly worked example to finish.
  • Pair with a confident partner for the guided practice.

Stretch

  • Explain a common mistake in writing and how to fix it.
  • Write a word problem that uses today's skill, then solve a partner's.

Homework and more practice

Free online practice with hints and printable worksheets for this skill: eurekami.com/math/grade-7.

Free lesson plan from eurekami.com/lesson-plan-builder

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Surface area of triangular prisms

Name

Date

Score/ 8

  1. Question 1

    A triangular prism has right-angled triangle ends with sides 8 cm, 15 cm and 17 cm. It is 11 cm long. Find its total surface area, in cm².

    15 cm8 cm17 cm

    Answer

  2. Question 2

    A tent-shaped prism has isosceles triangle ends: base 6 m, height 4 m and sloping sides 5 m. The prism is 3 m long. What is its total surface area, in m²?

    6 m5 m5 m

    Answer

  3. Question 3

    A triangular prism has right-angled triangle ends with sides 5 cm, 12 cm and 13 cm. It is 10 cm long. Find its total surface area, in cm².

    12 cm5 cm13 cm

    Answer

  4. Question 4

    A tent-shaped prism has isosceles triangle ends: base 12 m, height 8 m and sloping sides 10 m. The prism is 4 m long. What is its total surface area, in m²?

    12 m10 m10 m

    Answer

  5. Question 5

    A triangular prism has right-angled triangle ends with sides 10 cm, 24 cm and 26 cm. It is 12 cm long. Find its total surface area, in cm².

    24 cm10 cm26 cm

    Answer

  6. Question 6

    A tent-shaped prism has isosceles triangle ends: base 12 m, height 8 m and sloping sides 10 m. The prism is 3 m long. What is its total surface area, in m²?

    12 m10 m10 m

    Answer

  7. Question 7

    A triangular prism has right-angled triangle ends with sides 5 cm, 12 cm and 13 cm. It is 5 cm long. Find its total surface area, in cm².

    12 cm5 cm13 cm

    Answer

  8. Question 8

    A tent-shaped prism has isosceles triangle ends: base 12 m, height 8 m and sloping sides 10 m. The prism is 5 m long. What is its total surface area, in m²?

    12 m10 m10 m

    Answer

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Answer key: Surface area of triangular prisms

  1. 1. 560

  2. 2. 72

  3. 3. 360

  4. 4. 224

  5. 5. 960

  6. 6. 192

  7. 7. 210

  8. 8. 256