152
Multiplying a two-digit number
Textbook: Part 4, lesson 142, pp. 56–57
GoalUse multiplying two-digit numbers with units of length and mass and in problems.
New words
tens · o‘nlikones · birlikmass · massaweek · hafta
Explanation
When we multiply a quantity by a number, the unit stays the same: 64 cm × 4 = 60 × 4 + 4 × 4 = 240 + 16 = 256 cm. 23 kg × 8 = 20 × 8 + 3 × 8 = 160 + 24 = 184 kg. If there is a common factor in a problem, add first: 3 crates of tulips, 4 of daisies and 2 of roses, 45 flowers in each: (3 + 4 + 2) × 45 = 9 × 45 = 405.
Worked examples
45 dm × 5 = 40 × 5 + 5 × 5 = 200 + 25 = 225 dm.
Birds get 2 kg of seed a day: in one week 2 × 7 = 14 kg.
Class activity
“Shop accountant”: children are accountants working out the price of 3–9 items with a two-digit price: “5 loaves at 48 each”. They split the price into tens and ones to find the total.
Practice
1
3 × 46 = ?
138
2
62 × 5 = ?
310
3
4 × 92 = ?
368
4
74 × 5 = ?
370
5
3 crates of tulips, 4 of daisies and 2 of roses were brought to a garden. Each crate holds 45 flowers. How many flowers in all?
405
6
23 kg × 8 = how many kilograms?
184