July, 2009 | Maths Blog

Maths worksheet: Add decimals mentally (1)

At first glance you might reach for a pencil to do a sum such as 2.5 + 4.7. However, the Primary Framework for Maths suggests that children should be competent in adding two 2-digit numbers in their heads, and there is no reason why, with a little practice this can’t include adding two decimals. The most common approach is almost identical to adding tens and units.

Start by adding the largest digits, in this case the units: 2 + 4 = 6.

Then add the larger of the two tenths digits, which is 0.7, making 6.7.

Finally add on the 0.5, by counting on if necessary, making 7.2. Easy!

Add two decimals mentally (1)

There are, of course other approaches, such as adding 2 to the 4.7 to make 6.7, then adding the 0.5, which are equally good. It often depends on the numbers involved and any method which is quick and accurate is fine!

Maths Worksheet: Year 4 Count on Whole Tens

This worksheet looks at counting on in whole tens from 3-digit numbers, probably most suited for Year 4 children. There are a number of different strategies that children use to do this type of question. Some will count on in tens (still using fingers to record the number of tens they have counted). Others will use more efficient methods, such as, adding the tens digits and then adjusting the hundreds.

Count on whole tens

Year 6 Maths Worksheet: Rounding decimals

When rounding decimals to the nearest whole one the only digits that are crucial are the tenths – it does not matter what the hundredths or thousandths are.

When rounding a number such as 3.47 to the nearest whole number the key digit to look at is the tenths digit. If it is 5 or more, round up. Less than 5, round down.

So 3.44 rounded to the nearest whole one is 3.

3.47 rounded to the nearest whole one is 4.

Year 6 Rounding decimals (pg 1)

Data handling for year 4: Bar charts

It is a while since I have posted anything on data handling so here is a page on interpreting bar charts, which also uses the 24 hour clock. it is important to point out that charts such as these must have a proper title and that the axes must be labelled. When children produce their own bar charts they often forget to do this labelling.

When looking at a bar chart one of the first things to do is work out how the numbers are being represented. In this case the number of people on the bus is shown in blocks of 10 and half way between would be a block of 5.

Bar chart: buses

Coming soon: adding decimals, rounding and counting on in whole hundreds

Another week goes by and the summer term in the UK will soon be over. Meanwhile why not put a few minutes aside next week to dip into our latest worksheets. They will include pages on adding decimals mentally, and for year 6 a tricky page on rounding decimals. There is also a page coming up for year 4 on counting on in whole hundreds.

Maths Worksheet: Year 6 Order Decimal Fractions

$decimal-fractions-thousandths-y6$ It is not often that you see maths for primary school children which includes thousandths. But the justification is that in certain areas of measurement children might well come across them. For example there are 1000 metres in a kilometre so a distance might be written as 2.345 k, where the 5 is 5 thousandths of a kilometre. The same can be said of litres and ml. So decimal fractions including thousandths are here to stay!

Once again, when looking at ordering numbers it is the digits to the left which are most important e.g. 0.1 is bigger than 0.09.

Again the hardest question here is probably the last: being able to write a number bigger than 0.09 but smaller than 1. An easy way to do this is to keep the hundredths digit the same and a thousandth is added e.g. 0.091. Of course 0.0900000000000001 would do equally well and some children like to explore these possibilities.

Decimal fractions thousandths y6 pg 1

Maths Worksheet: Year 5 Order Decimal fractions

$order-decimal-fractions-y5-p1$ By year 5 children should be getting familiar with numbers with two decimal places. Money is the obvious example, but they should also be using these numbers out of the context of money. The main development is with the use of the second digit after the decimal point; the hundredths.

When writing a number such as 4 hundredths it is important to include both zeros in the units and the tenths: 0.04. The zero is placed in the units to make it easier to see that it is a decimal fraction; otherwise the decimal point might be missed and the number read as 4.

Probably the hardest question on this page is the last, to write a number between 0.9 and 1.

Whilst some children will deny that it is possible, there are, of course, millions of possible answers, but usually we would expect children to keep to writing hundredths e.g. 0.92 or 0.94.

Order decimal fractions y5 p1

Coming soon: Subtraction and decimal fractions

Next week we have a new worksheet on using the subtraction sign, suitable for Year 1 children and, for those slightly older, a page on pairs of numbers that make 20. Knowing facts such as the pairs of numbers that make 20 are important for children to learn. We often go on about the importance of learning tables but these other facts are just as vital to give confidence with mental arithmetic.

We also have two pages on ordering decimal fractions for Year 5 and Year 6. The first looks at tenths and hundredths. A good test of children’s understanding of decimals is to ask them to write a number between two other decimal fractions. eg write a number between 0.9 and 1.

The year 6 decimal fraction worksheet takes a closer look at thousandths, which are important to understand in the context of measurement eg 1000 ml in a litre, or 1000 metres in a km.

Maths Worksheet: Year 4 Find a Difference

Sometimes a simple question can reveal a great deal about how children deal with numbers. This maths worksheet on finding differences is full of such questions.

Let’s look at 3005 – 8 which is easier to do mentally than on paper.

There are several ways that this can be done.

1. Count down, one at a time, 8 from 3005, saying each number as you go. Fingers may be held up on each count down until 8 is reached.

3004, (1), 3003 (2), 3002 (3), 3001 (4), 3000 (5), 2999 (6), 2998 (7), 2997 (8)

2. A different way is to take the 8 from 3000, then add 5.

3000 – 8 = 2992

2992 + 5 = 2997

3. A third way is to take 5 off the 8 leaving 3.

Then take 3 off 3000 = 2997

It is well worth talking to children about how they do this kind of question and what strategies they employ. Much will depend on their knowledge of number.

Find a difference by counting up (pg 1)