24
Multiplying round numbers
Textbook: Part 1, lesson 24, pp. 75–77
GoalLearn how to multiply round numbers.
New words
round number · yaxlit sonnumber of zeros · nollar soniproduct · ko‘paytmabanknote · kupyura
Explanation
To multiply two round numbers, first set aside the zeros at their ends, multiply the remaining numbers, then write at the end of the result as many zeros as both factors had together. For example 30 × 70 = (3 × 10) × (7 × 10) = (3 × 7) × (10 × 10) = 21 × 100 = 2 100.
Worked examples
9 000 × 300: 9 × 3 = 27, zeros: 3 + 2 = 5. Answer: 2 700 000.
20 × 40 = 2 × 4 × 100 = 800; 60 × 8 000 = 6 × 8 × 10 000 = 480 000.
Class activity
“Count the zeros”: in pairs, children say two round numbers. The partner first says how many zeros the product has, then the product. If the answer has more than 5 zeros, the points are doubled.
Practice
1
300 × 90 = ?
27000
2
60 × 8 000 = ?
480000
3
7 × 50 000 = ?
350000
4
A bundle has 80 notes of 50 000 so‘m. How much money is in the bundle?
4000000
5
Calculate: 20 × 30 + 60 × 70.
4800
6
40 × x = 2 800. Find x.
70