Условие:

Вычислите устно.
24 * 2
40 : 40
360 : 60
180 : 90
490 – 1
230 * 3
17 * 10
800 : 100
64 + 16
900 – 400
9 * 80
60 * 5

24 * 2 = 48
40 : 40 = 1
360 : 60 = 6
180 : 90 = 2
490 – 1 = 489
230 * 3 = 690
17 * 10 = 170
800 : 100 = 8
64 + 16 = 80
900 – 400 = 500
9 * 80 = 720
60 * 5 = 300
Вычисления:
24 * 2 = (20 + 4) * 2 = 20 * 2 + 4 * 2 = 2 * 2 * 10 + 4 * 2 = 40 + 8 = 48
40 : 40 = 40 : 4 : 10 = 10 : 10 = 1
360 : 60 = 360 : 6 : 10 = 60 : 10 = 6
180 : 90 = 180 : 9 : 10 = 20 : 10 = 2
490 – 1 = 489
230 * 3 = (200 + 30) * 3 = 2 * 3 * 10 * 10 + 3 * 3 * 10 = 6 * 10 * 10 + 9 * 10 = 60 * 10 + 90 = 690
17 * 10 = 170
800 : 100 = 800 : 10 : 10 = 80 : 10 = 8
64 + 16 = 64 + 10 + 6 = 74 + 6 = 80
900 – 400 = 500
9 * 80 = 9 * 8 * 10 = 72 * 10 = 720
60 * 5 = 6 * 5 * 10 = 30 * 10 = 300