Video: Solving Word Problems on Unit Rate That Involve Decimals

A car uses one litre of petrol to travel 10 kilometres. How many litres of petrol will be used on a journey of 676.8 kilometres?

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Video Transcript

A car uses one litre of petrol to travel 10 kilometres. How many litres of petrol will be used on a journey of 676.8 kilometres?

Having read this question, we can see that one litre of petrol is used for every 10 kilometres that a car travels. We are asked to calculate how many litres of petrol will be used on a journey of 676.8 kilometres. To find the answer, we need to find how many lots of 10 kilometres there are in this long distance. In other words, we need to find the answer to 676.8 divided by 10. We know that 676.8 consists of six hundreds, seven tens which have a value of 70, six ones, and eight-tenths.

And when we’re thinking about the place value of a number, each column to the right of another number is worth 10 times less. So, for example, 10 times less than a hundred is a ten. 10 times less than a ten is a one, and so on. So, if we want to divide 676.8 divided by 10, what we really want to do is for each digit in that number to be worth 10 times less.

In other words, they all need to shift one place to the right. 10 times less than eight-tenths is eight hundredths. 10 times less than six ones is six-tenths. 10 times less than seven tens, is seven ones. And if we divide six hundreds by 10, we get six tens. 676.8 divided by 10 is 67.68.

If a car uses one litre of petrol to travel 10 kilometres, we can find the number of litres of petrol that will be used on a journey of 676.8 kilometres by dividing this number by 10. We managed to divide 676.8 by 10 by shifting the digits one place to the right. Our answer contains the same four digits; they’ve just moved. The number of litres of petrol that will be used on a journey of 676.8 kilometres is 67.68 litres.

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