The Transport Museum
Multiples of 10 and 100
Multiply by multiples of 10 and 100, using bus seats.
In your book, Maths Mela (Chapter 13, The Transport Museum), a small bus can seat 20 people. How many people can sit in 12 buses? We need 12 × 20. Three children solve it in three ways.
One says: 12 × 20 = 10 × 20 and 2 × 20 = 200 + 40 = 240. Another says: 12 × 20 = 12 × 10 and 12 × 10 = 120 + 120 = 240. The third says: 20 is 2 tens, so 12 × 20 = 12 × 2 tens = 24 tens = 240. All three get 240 people!
The tens way is quick. 16 × 20 = 16 × 2 tens = 32 tens = 320. 13 × 30 = 13 × 3 tens = 39 tens = 390. 43 × 60 = 43 × 6 tens = 258 tens = 2580. 70 × 80 = 70 × 8 tens = 560 tens = 5600.
Hundreds work the same way. 11 × 200 = 10 × 200 and 1 × 200 = 2000 + 200 = 2200. Or: 200 is 2 hundreds, so 11 × 200 = 11 × 2 hundreds = 22 hundreds = 2200. Also 23 × 200 = 46 hundreds = 4600, 14 × 300 = 42 hundreds = 4200, and 7 × 800 = 56 hundreds = 5600.
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