Video: KS2-M18 • Paper 2 • Question 17

There are 28 pupils in a class. The teacher has 8 liters of orange juice. She pours 225 milliliters of orange juice for every pupil. How much orange juice is left over?

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Video Transcript

There are 28 pupils in a class. The teacher has eight liters of orange juice. She pours 225 milliliters of orange juice for every pupil. How much orange juice is left over?

The question asks us to calculate how much orange juice is left over. To do this, first, we need to work out how much orange juice the pupils have drunk. We know there are 28 pupils. And the teacher pours 225 milliliters of juice for each pupil. We need to multiply 225 by 28 to find out how much juice the pupils have drunk.

We’re using long multiplication to find this answer. And we’re going to start by multiplying 225 by eight. Five times eight is 40. Two times eight is 16, plus the four we exchanged gives us 20. Two times eight is 16, plus the two we exchanged gives us 18. 225 multiplied by eight is 1800.

Next, we need to multiply 225 by 20. Multiplying by 20 is the same as multiplying by 10 and then by two, which is what we’re going to do. By writing a zero in the ones place, we’re moving the digits one place to the left into the tens column. Now, let’s multiply by two. Five times two is 10. Two times two is four, plus the one we exchanged gives us five. And our final digit, two times two is four. 225 multiplied by 20 is 4500.

Now we just need to add our two totals together to tell us what 225 times 28 is. First, we need to add in the ones column. Zero and zero gives us a total of zero. And we have the same in the tens column giving us a total of zero. Eight plus five is 13. Finally, we need to add in the thousands column. One and four is five, plus the one we exchanged gives us six. 225 multiplied by 28 is 6300. This means that the pupils drank 6300 milliliters of orange juice.

Now, we can work out how much juice is left over. To do this, we need to find the difference between eight liters and 6300 milliliters. Or, we need to subtract 6300 milliliters from eight liters. But first, we need to convert the liters into milliliters. One liter is equal to 1000 milliliters. So eight liters is equal to 8000 milliliters.

To find the difference, we can count on from 6300 to 8000. If we add 700 to 6300, that will take us to 7000. Then, we can add 1000 to take us to 8000. Altogether, we added 1700. So the amount of orange juice leftover is 1700 milliliters, which we could also write as 1.7 liters.

To find the answer, the first step was to calculate how much juice the pupils had drunk by multiplying 225 by 28. Then, we could subtract this amount from the eight liters of juice the teacher had to begin with. But first, we converted liters to milliliters. We subtracted 6300 from 8000 to give us the answer 1700 milliliters of orange juice leftover.

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