Multiplication by
heart (by numbers 10,100,1000)
1. The product of what numbers are 20,40,80,100?
20 = ............... = ............... = .............. = ............... = ............... = ...............
40 = .............................................................................................................
80 = .............................................................................................................
100 = .............................................................................................................
2. Explain how these products are calculated.
10 · 12 = 10 · (10 +2) = 10 · 10 + 10 · 2 = 100 + 20 = 120
10 · 225 = 10 · (200 + 20 + 5) = 2 000 + 200 + 50 = 2 250
10 · 4 780 = 10 · (4 000 + 700 + 80) = 40 000 + 7 000 + 800 = 47 800
100 · 50 = 100 · (10 · 50) = 10 · (100 · 5) = 10 · 500 = 5 000
100 · 1 426 = (10 · 10) · 1 426 = 10 · (10 · 1 426) = 10 · 14 260 = 142 600
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If I multiply by 100 I add two noughts at the end of the number. |
3.10 pairs of shoes were bought to the theatre.The prize of one pair was 325 kroons.How much money was spent?
The answer
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4. Calculate by heart! If you subtract from the biggest product the sum of other products you get the answer 1000. |
69 · 100 = .......... 150 · 10 = .......... 34 · 100 = .......... 10 · 100 = .......... |
5. Write down the unit of length 10 times longer than:
1) a decimetre
2)
a millimeter
3)a centimetrea .....................................
6. Write down the unit of length 100 times longer than:
1)a millimetre
2)a centimetre
.
1 000 · 5 = (10 · 100) · 5 = 10 · (100 · 5) = 10 · 500 = 5 000
1 000 · 34 = (10 · 100) · 34 = 10 · (100 · 34) = 10 · 3 400 = 34 000
If I multiply a number by 1000
.