Question Video: Deducing Information about Patterns Involving Symbols Mathematics • 5th Grade

Complete the pattern: 2.7, 1.9, 1.1, _.


Video Transcript

Complete the pattern: 2.7, 1.9, 1.1, what.

The pattern that we’ve been given here involves decimal numbers. We have three decimal numbers and then a missing number, which is the number we need to find to complete the pattern. Looking for patterns in decimal numbers is not always very easy to do. We’re not always used to thinking in terms of tenths and hundredths and so on. One method that we could use to help us is to write each number without the decimal point. Really, this is the same as multiplying each decimal by 10, shifting the digits one place to the left.

So 2.7 would become 27, 1.9 would become 19, and 1.1 would become 11. Our reason for doing this is that we’re now dealing with whole numbers. And it might be easier to spot a pattern this way. The pattern is certainly decreasing. And to get from 27 to 19, we’d need to subtract eight. And if we subtract eight from 19, we get 11. So we can see this idea of subtracting eight each time is the rule for the whole sequence. So the missing number in this whole number sequence will be the answer to 11 take away eight, which, of course, is three.

Now, we can use everything that we’ve just found out and apply it to our pattern of decimals. Everything remains the same, except it’s worth 10 times less. Remember, we multiplied each decimal by 10 and made it a whole number. So everything became 10 times greater. We said the rule for our whole number pattern was to subtract eight. So the number we need to subtract for our decimal pattern needs to be 10 times less than eight. This is eight-tenths or 0.8.

So the missing number in our problem is going to be the answer to 1.1 take away 0.8. Instead of three, the answer is going to be 10 times less than three. So the answer is going to be 0.3. Our completed pattern is 2.7, 1.9, 1.1, 0.3. The missing number that we used to complete the pattern was 0.3.

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