Multiplying and Dividing
Multiplying larger numbers
Multiply a three-digit number by a single digit, and a two-digit number by a two-digit number.
A big multiplication is several small ones stacked together. Nobody knows 234 × 3 by heart, but everybody can do 200 × 3, 30 × 3 and 4 × 3 — and adding those three answers gives the whole thing. Splitting a number into its hundreds, tens and ones like this is called partitioning, and it turns one hard question into three easy ones.
Every part gets multiplied
When both numbers are big, every part of the first has to meet every part of the second. For 23 × 14 that is 23 × 10 and 23 × 4 — miss one and the answer comes out short. The commonest slip in this whole topic is multiplying by the 1 in 14 instead of by the ten it stands for.
Worked example
Work out 234 × 3.
200 × 3 = 600.
Two hundreds times three is six hundreds — the times table you know, wearing bigger clothes.
Try it together
Now let us do 23 × 14 together.
Split the 14 into 10 and 4, and take the twenty-threes in two goes.
1.First the tens. What is 23 × 10?
Have a go
Have a go on your own: 213 × 4 = ?
Hint: Two hundreds, one ten and three ones, each multiplied by four.
Ready to practise?
Eight questions on what you have just read. Nothing is timed, and you can play as many times as you like.