33
Multiplying round numbers (column method)
Textbook: Part 1, lesson 33, pp. 102–104
GoalMultiply round numbers in a column using the significant part of a number.
New words
significant part · qiymatli qismround number · yaxlit sonzeros · nollarcolumn · ustun
Explanation
If we drop the zeros at the end of a number, what is left is its significant part. For example, the significant part of 4 050 600 is 40 506. To multiply round numbers we multiply the significant parts and then write after the result all the zeros from the ends of both factors.
Worked examples
340 × 2 100: 34 × 21 = 714, zeros: 1 + 2 = 3. Answer: 714 000.
6 300 × 150: 63 × 15 = 945, zeros: 2 + 1 = 3. Answer: 945 000.
Class activity
“Find the significant part”: cards show round numbers with 5–7 digits. Children circle the significant part, then multiply two cards in a column.
Practice
1
36 × 52 000 = ?
1872000
2
81 000 × 4 = ?
324000
3
3 000 000 × 30 = ?
90000000
4
A theatre ticket costs 28 000 so‘m for a child and 12 000 so‘m more for an adult. How much is paid for 40 children and 30 adults?
2320000
5
A car uses 8 l of petrol per 100 km. How many litres are needed for 300 km?
24