(100 × 90 = 9,000)
( 400 × 10 = 4.000)
(60 × 50 = 3.000)
(30 × 20 = 600)
(700 × 4 = 2,800)
(10 × 45 = 450)
How should we write 450 in the table below?
Solution:
Solution:
Let us fill in the table and observe the patterns.
Solution:
NCERT Textbook Pages 75-76
Doubling and Halving
Butter packets are arranged in the following ways. Let us find some strategies to calculate the total number of packets.
(c) Solve the following problems like the previous ones.
Solution:.
This halving and doubling strategy works well when we have to multiply with numbers like 5 and 25. Discuss why?
Solution:
No, for such numbers like 5 and 25, we need to change our strategy, as we cannot half those numbers, as they are odd and can make the calculation even complicated.
(d) Find the product by halving and doubling either the multiplier or the multiplicand.
1) 5 × 18
2) 50 × 28
3) 15 × 22
4) 25 × 12
5) 12 × 45
6) 16 × 45
Solution:
(e) Give 5 examples of multiplication problems where halving and doubling will help in finding the product easily. Find the products as well.
Solution:
NCERT Textbook Page 76
Nearest Multiple
(c) Give 5 examples of problems where you can use the nearest multiple to find the product easily. Find the products as well.
Solution:
(1) 5 × 31 = 5 × 30 + 5 = 150 + 5 = 155
(2) 7 × 29 = 7 × 30 – 7 = 210 – 7 = 203
(3) 12 × 49 = 12 × 50 – 12 = 600 – 12 = 588
(4) 8 × 101 = 8 × 100 + 8 = 800 + 8 = 808
(5) 16 × 99 = 16 × 100 – 16 = 1600 – 16 = 1584
(Answer may vary)
(d) Find the products of the following numbers by finding the nearest multiple.
(1) 7 × 52
(2) 12 × 28
(3) 75 × 31
(4) 99 × 15
(5) 8 × 25
(6) 22 × 42
Solution:
(1) 7 × 52 = 7 × 50 + 7 × 2 = 350 + 14 = 364
(2) 12 × 28 = 12 × 30 – 12 × 2 = 360 – 24 = 336
(3) 75 × 31 = 75 × 30 + 75 = 2250 + 75 = 2325
(4) 99 × 15 = 100 × 15 – 15 = 1500 – 15 = 1485
(5) 8 × 25 = 10 × 25 – 2 × 25 = 250 – 50 = 200
(6) 22 × 42 = 22 × 40 + 22 × 2 = 880 + 44 = 924
NCERT Textbook Page 77
Let Us Solve
Use strategies flexibly to answer the following questions. Discuss you thoughts in class.