🔵Multiplying Tens and Ones
To multiply a 2-digit number by a 1-digit number, multiply the ones first, then the tens, and add the results.
Example: 23 × 3 → 3 × 3 ones = 9 ones, and 3 × 2 tens = 6 tens (60). So 60 + 9 = 69.
👀 See a worked example
Multiply 14 × 2.
- Ones: 2 × 4 = 8
- Tens: 2 × 10 = 20
20 + 8 = 28.
Multiply 31 × 3.
Ones: 3 × 1 = 3; Tens: 3 × 30 = 90. So 31 × 3 = 93.
🤖 Vidi's Key Points
- Multiply the ones first, then the tens.
- Add the two results to get the answer.
- 23 × 3 = (3 × 3) + (3 × 20) = 9 + 60 = 69.
🟢Multiplying with Carrying
When the ones multiply to 10 or more, we carry the tens, just like in addition.
Example: 27 × 4 → 4 × 7 = 28, write 8 and carry 2. Then 4 × 2 tens = 8 tens, plus the carried 2 = 10 tens. So the answer is 108.
In a word problem, 'each', 'every' and 'times' usually mean multiply.
👀 See a worked example
Multiply 16 × 5.
5 × 6 = 30 → write 0, carry 3. 5 × 1 ten = 5 tens + 3 = 8 tens. So 16 × 5 = 80.
There are 25 pencils in a box. How many in 3 boxes?
'In each box' → multiply: 25 × 3 = 75 pencils.
🤖 Vidi's Key Points
- If the ones multiply to 10 or more, carry the tens.
- Add the carried tens to the tens product.
- 'Each', 'every' and 'times' usually mean multiply.
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