Crimlin, Castlebar, Co. Mayo, F23 V008

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##### MATHS - MATAMAITIC

Suggested Website: IXL.com

It is best to establish a routine and follow it each time you approach a sum.

1. Look at the number on the top row. Say aloud: "Eighty six".

2 Look at the number on the bottom row. Say aloud: "Fifty seven".

3. Say aloud: "Eighty six take away fifty seven".

4. In your head, do a quick estimate of what the answer will be, like this: round 86 to 90, then round 57 to 60. Subtract 60 from 90; that's 30. So the correct answer should be around 30.

5. Look at the units column. Can you take 7 from 6? No. So you must regroup eighty six.

At the moment, it's written as 8 tens and 6 units. Change it to 7 tens and 16 units.

6. Now take 7 units from 16 units, and take 5 tens from 7 tens.

8. Say "Eighty six take away fifty seven equals twenty nine."

9. Think back to your estimate, which was 30... very near to 29.

In this second example, you can follow the same routine as above.

When it comes to rounding 176, look at the tens and units. Round 76 to 80, and say "One hundred and 180". Round 149 to 150. Now it's easy to take 150 from 180.

The correct answer should be around 30.

Note: When subtracting, always work on the units column first, then work on the tens column and finish with the hundreds column.

# Subtraction (continued)

In this example, we see that we must regroup €1.35. (Because 8 units cannot be taken from 5 units.)

Before you do any regrouping, look at the tens column.

You'll be taking a big number on the bottom from a smaller number on the top....

So when you regroup €1.35, say "Instead of 13 tens and 5 units, I'll group it as 12 tens and 15 units".

( 1 hundred is 10 tens. 13 tens is really 1 hundred and 3 tens. )

Draw a line straight through 13 and write 12 in the tens column.

Write 1 beside 5.

First, do the subtracting on the units column.

Then on the tens column, take 6 from 12.

Lastly, on the hundreds column, 1 is no longer there. So you're taking 0 from 0.

Keep the decimal points in a column, one directly under the other. (They're not really under each other in the picture.....sorry.)

Put the Euro sign in to show that you're working with Euros.

###### Pack a box.

Take a Cornflakes box.

Stand it upright. Measure the sides and write the measurements in your copy.

Look at the opening at the top, to get an idea of how big it is.

Now look at the space inside the box, to get an idea of how big that is.

Think about the things that you measured yesterday. Look at the sketches that you made in your copy.

Try to guess how many of them would fit in the Cornflakes box.

Write in your copy: I think .... and..... and...... and....would fit in the Cornflakes box.

Now pack all those things into the Cornflakes box. Do they fit?

(You could take them out and try putting them in again in a different way. They might fit better.)

Now write in your copy: The ....and the..... and the...and the... fit in the Cornflakes box.