This is classroom session taught by Yeap Ban Har on Day 1 of WSU Singapore Math Summer Institute. More than 70 participants took part in this institute - the second one in this university.
16. Find the value of 28 x 32 .
To see 28 as 20 and
8 and 32 as 30 and
2.
This leads to the
idea of (a + b)(c +
d).
18. x
Use the digits 0 to 9 no more than once
to make a correct multiplication
sentence.
The class had four solutions
32 x 15 = 480
12 x 65 = 780
12 x 48 = 576
39 x 12 = 468
12 x 43 did not work.
19. 12 can be seen as 10 and 2.
Thus, 12 x 65 can also be computed as the sum of 10 x 65 and 2
x 65 i.e. 650 + 130.
12 can be seen as 10 and 2.
Thus, 39 x 12 can also be computed as the sum of 39 x 10 and
39 x 2 i.e. 390 + 78.
Alternatively, 40 x 12 can be used to compute 39 x 12.
The use of number bonds to compute large numbers gives
students opportunities to develop their number sense.
20. Find the value of 7081 3.
Using number bonds, 7081 is
6000, 900, 180 and 1. Each is
then divided by three.