Lesson video

Hello, my name is Miss Parnham.

In this lesson, we're going to learn how to round to two decimal places.

Decimal places mean numbers after the decimal point.

So numbers with two decimal places have two numbers after the decimal point.

So let's inspect these numbers and identify which ones have two decimal places.

The first number a 41.

28 has two digits after the decimal point, therefore it has got two decimal places.

The next number is 25.

This just contains two digits.

There is a decimal point here, but we don't write it because this is an integer.

So this number does not have two decimal places.

Next, we have 0.

012.

This has three decimal places, even though there are two non-zero digits, there are still three numbers after the decimal point.

So this does not have two decimal places.

1.

08 does have two digits after the point.

So this does have two decimal places.

2,335,000.

93 has two digits after the decimal point and has therefore got two decimal places.

Let's round some numbers to two decimal places.

Let's take a look at 23.

456.

If we are rounding to two decimal places, we just need to keep the first two digits after the decimal point.

Let's place a line there.

We don't just truncate this number or chop it off.

We look at the next number after that line which is the third decimal place to tell us what to do, because this number lies between 23.

45 and 23.

46.

But this six in the thousandths position tells us that it is slightly nearer to 23.

46.

So this number rounds up, because that digit after the line is five or greater.

Let's look at 10.

3256.

Yes, this number has four decimal places, but because we are rounding to two decimal places, we're still only concerned about looking at the third decimal place in order to decide what to do.

That number is five or bigger.

Because it's five and therefore this round to 10.

33 to two decimal places.

The next number has again got four decimal places, but because we need to keep two decimal places, we are only required to look at the third decimal place to make that decision for us.

This number is five or bigger because it's nine.

Therefore this number rounds up to 365.

06.

Now we have 0.

6726.

Again, we placed that number after the second decimal place.

I look to the third decimal place, which is a two.

This tells us to round the number down.

So the answer is 0.

67.

We don't move any digits down.

We are rounding down, because 0.

67 is less than 0.

6726.

Here are some questions for you to try.

Pause the video to complete the task and restart the video when you're finished.

Here are the answers.

There are few things that you might've noticed here.

In part C, we have an answer of 0.

40.

Now, some people might be tempted to emit that zero in the second decimal place, but we've been asked for two decimal places, so we gave two decimal places.

And that leads me on to part D.

That decimal was considerably smaller than the other numbers there and it meant that it rounded to 0.

00.

So that that example sort of highlights the limitations of rounding in two decimal places.

And then the last two parts of this question, F and G have both had nines being rounded up.

And that meant that the next column increased by one and where the nine had been that was replaced by zeros.

So, hence we have those answers one with two zeros in the decimal place and then one with the second decimal place being a zero.

Let's look at this problem.

Sophie is working out the area of the triangle to two decimal places.

What mistake has she made? She has the right area formula for the triangle, but look, she's input her rounded answers into the work end.

What Sophie should have done is worked with the accurate numbers that were given on the diagram and then rounded to two decimal places at the end.

She should have got the answer of 44.

17.

Here are some questions for you to try.

Pause the video to complete the task and restart the video when you're finished.

Here are the answers.

If you notice here, we have another example of rounded numbers having zero in the second decimal place for parts B and D, as we discussed before.

That's perfectly right and what we should do.

And you may have noticed that I got you to use the squared key and the square root key on your calculator.

Always good to practise using these keys on the calculator.

Here is another question for you to try.

Pause the video to complete the task and restart the video when you're finished.

Here are the answers.

Now, hopefully you didn't make the mistake that Sophie made and you worked with the numbers that were provided and then rounded at the end.

But you may have come a little bit unstuck with the triangle.

One of those lens was not required to work out the area.

The area of the triangle is height multiplied by base divided by two, and the height and base must be perpendicular.

So we needed to use 9.

786 and 4.

089 in that calculation.

Here is a further question for you to try.

Pause the video to complete the task and restart the video when you're finished.

Here are the answers.

Did you get both mistakes? Amir did Sophie's trick again and rounded numbers before calculating with them.

Never, ever do none of that.

And in fact, if you calculate with the number and then go on to further problems with that number never worked with a rounded answer, always keep the full, accurate answer in your calculator and you may write down rounded answers, but you must calculate with full, accurate answers.

And Eva, she forgot to round at the end, so she would lose some marks there.

That's all for this lesson.

Thank you for watching.