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Lesson 17 of 144 · Monday · 🩺 The Human Body
Multiply with an area model
I can multiply 2-digit numbers with an area model
Warm-up
Facts race: 6 × 7, 8 × 9, 7 × 12, 40 × 3, 60 × 50. (42, 72, 84, 120, 3,000)
Start here
Say this
Put two fingers on the side of your neck and count your heartbeats for 30 seconds while I time you. Double it: that's your beats per minute. If a heart beats 84 times a minute, how many beats in a 45-minute practice? Today we'll draw a picture that makes big multiplying easy: the area model.
Teach it: touch it, draw it, write it
1 · Hands on
Build 13 × 12 as a rectangle of base-ten blocks (or paper cutouts): 1 flat (100), 5 rods (10 each) and 6 cubes (1 each). Count it up: 156.
2 · Draw it
Draw a box for 24 × 36. Split 24 into 20 + 4 across the top and 36 into 30 + 6 down the side. Fill the 4 parts: 600, 120, 120, 24.
3 · Numbers
Add the partial products (the answer from each part): 600 + 120 + 120 + 24 = 864. So 24 × 36 = 864.
Try it together
- 1
23 × 14 (draw an area model)
Show answerAnswer
322 (200 + 80 + 30 + 12)
- 2
45 × 32
Show answerAnswer
1,440 (1,200 + 80 + 150 + 10)
- 3
A nurse counts 18 breaths a minute. How many breaths in 45 minutes?
Show answerAnswer
810
- 4
An adult's resting heart beats about 70 times a minute. About how many in 15 minutes?
Show answerAnswer
About 1,050 beats
On their own
✏️ Draw an area model for each problem. Add the parts to find the product (the answer to a times problem).
- 1
20 × 30 = ?
- 2
40 × 16 = ?
- 3
Fill in the area model for 23 × 14: 20 × 10 = ___, 20 × 4 = ___, 3 × 10 = ___, 3 × 4 = ___. What is the total?
- 4
32 × 21 = ?
- 5
45 × 32 = ?
- 6
67 × 28 = ?
- 7
Compare with <, > or =: 36 × 25 ___ 29 × 31
- 8
An area model has 4 parts: 800, 120, 60 and 9. What multiplication problem made it, and what is the product?
- 9
Maya's heart beat 84 times a minute while she read. How many times did it beat in 45 minutes of reading?
- 10
A school nurse has 24 boxes of bandages with 36 bandages in each box. How many bandages does she have?
- 11
Each lung checkup takes 15 minutes. Dr. Patel does 26 checkups a week. How many minutes is that? Is it more or less than 6 hours?
- 12
A clinic orders 48 boxes of tongue depressors with 25 in each box and 12 boxes of gloves with 50 in each. How many items in all?
- 13
Explain: why does the area model for 23 × 14 have 4 parts?
⭐ Star problem
Use the digits 3, 4, 6 and 8 once each to make two 2-digit numbers with the greatest possible product. What is it?
Play it
Area Model Race. Take out the 10s and face cards (ace = 1). Flip 4 cards and make two 2-digit numbers, like 36 and 52. Both players draw the area model and find the product. The first correct answer earns a point, plus a bonus point for a product within 500 of 2,000. First to 7 points wins.
In real life
Area models are real! Builders and flooring stores find a room's area by multiplying length times width. Task: measure a room in feet (round to whole feet), draw it as an area model, and find its area in square feet. If carpet cost $4 a square foot, what would carpeting that room cost?
Exit ticket
One question, no help. It tells you it stuck.
34 × 26 = ?
Show answerAnswer
884 (600 + 180 + 80 + 24)
Every school day is like this
A real lesson in math and in reading, every day, at each kid's level
- ✏️ 144 lessons and 36 Friday checks a year in each subject
- 🧭 A ten-minute placement quiz to find the right start
- 🔬 A science and history unit every afternoon, for the whole family
- 🌎 Real World Friday: a project that leaves the house every month
- 🎨 Electives, reading lists and printable binders
- ☀️ A get-ready August and a light summer review