Video Transcript
Calculate the following: 1.28 divided by four.
In this question, we need to divide a decimal by an integer or a whole number. One method we could use is short division. We need to find out how many fours there are in 1.28. Now using short division like this is exactly the same method as when we divide two whole numbers. The only difference is we need to make sure our answer has a decimal point in it.
Firstly, how many fours are in one? Well, the answer is zero. And we still have a remainder of one so we’ll cross through the one and write it next to the two. How many fours are in 12? We know three fours are 12 — four, eight, 12. And there’s no remainder, so we can just look at the last digit. How many fours in eight? There are two fours in eight. And so 1.28 divided by four equals 0.32 or 32 hundredths. That was a quick method. Let’s go through another strategy we could use that’s just as quick.
This one involves partitioning. We can start by breaking up our decimal into the whole number and its decimal part. And so 1.28 is the same as one and 0.28. A good strategy for dividing by four is to halve, then halve again. Let’s use this strategy to divide our two parts by four. Half of one is 0.5. And half of 0.5 is the same as a quarter; it’s 0.25. So we know one divided by four equals 0.25.
Now, let’s divide 0.28 using the same method. Half of 0.28 or 28 hundredths equals 14 hundredths or 0.14. And then half of 14 hundredths equals seven hundredths or 0.07. And so 0.28 divided by four equals 0.07. We’ve divided both parts of the number by four. Now, we just need to add our two answers together. Five hundredths and seven hundredths equals 12 hundredths. Two tenths plus zero tenths equals two tenths. But we’ve also exchanged to tenth that equals three tenths. And there’s nothing to add in the ones place. The answer is exactly the same as when we use short division. 1.28 divided by four equals 0.32.
