decimals | Maths Blog

Resource of the Week: Decimals that make 10

Here we have mental arithmetic maths worksheet on decimals, most suitable for Year 5. This page looks at pairs of decimals that make 10. Once again there are several ways of tackling these questions.

One way is to add on from the smaller number, firstly, the tenths to make the next whole number, and then the units to make 10.

eg 10 – 6.7

Count on from 6.7 to 7 which is 0.3

Then count on from 7 to 10 which is 3

Answer 3 + 0.3 = 3.3

Another way is to count on the units first and then the tenths, but beware the answer which counts on 4 from 6 to make 10 and than counts on 0.3 as this will result in an answer which is one too many: a common slip-up.

Another way of doing this is to ignore the decimal and think of the question as 100 – 67. Work it out mentally (which is 33) and then convert back to 3.3.

Decimals with a total of 10

Resource of the Week: Adding decimals mentally

Mental arithmetic is the key to success with calculating. 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. Continue reading “Resource of the Week: Adding decimals mentally”

Maths worksheet: Add decimals mentally (2)

This is a follow up page to an earlier worksheet on adding decimals mentally. The approach is probably the same as adding 2-digit numbers, in that most people seem to do these ‘in their head’ by adding the units first and then adding on the decimals.

So, with 4.6 + 3.5 my thinking would probably go along the lines of:

‘4 + 3 is 7, making 7.6 plus point 5 which is 8.1’.

It is not the only approach, but is usually a very effective one.

Add two decimals mentally (2)

Year 6 maths worksheet: Reading decimal fractions (2)

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This is a follow up page from one published earlier, reinforcing reading decimal fractions.

It is important that children reading decimals correctly. With a decimal such as 0.345 probably the best way to read it is: ‘nought point three, four, five and not nought point three hundred and forty five.

This is also good revision of place value and the use of thousandths. Probably children will come across thousandths only in terms of measurement such as litres and ml, or kilometres and metres.

Reading decimal fractions (2)

Year 6 Maths Worksheet: rounding decimals

The second in our series on rounding decimals for year 6, this worksheet looks at rounding to the nearest whole number and to the nearest tenth.

When rounding to the nearest whole number, the crucial digit to look at is the tenths digit. If it is 5 or more then the units will round up; if it is less than 5 the units will remain the same.

When rounding to the nearest tenth the crucial digit to look at is the hundredth.
Difficulties can occur when a number that needs rounding up also changes the units and possibly the tens digits. For example 9.95 rounded up to the nearest tenth is 10.

Rounding decimals (pg 2)

Maths Worksheet: Decimals with a total of 10

Another mental arithmetic maths worksheet on decimals, suitable for Year 5. This page looks at pairs of decimals that make 10. Once again there are several ways of tackling these questions.

One way is to add on from the smaller number, firstly, the tenths to make the next whole number, and then the units to make 10.

eg 10 – 6.7

Count on from 6.7 to 7 which is 0.3

Then count on from 7 to 10 which is 3

Answer 3 + 0.3 = 3.3

Another way of doing this is to ignore the decimal and think of the question as 100 – 67. Work it out mentally (which is 33) and then convert back to 3.3.

Decimals with a total of 10

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 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

Maths Worksheet: Decimal Fractions, hundredths

$decimal-fractions-hundredths-y5$ Reading decimal fractions can get quite tricky when moving into hundredths and this maths worksheet is a good test of understanding, probably most suited for year 5 children (/10 yrs old).

0.24 can be read as 24 hundredths or 2 tenths and 4 hundredths. As a fraction it would be written as 24/100.

With a number such as five and three hundredths it is important to keep the zero in the tenths so that it is written as 5.03.

Watch out for a common mistake on a question such as twelve hundredths when children write 0.012; the one digit has been placed in the hundredths column when it should be in the tenths with the 2 digit in the hundredths.

Decimal fractions: hundredths (pg 1)

Multiplying decimals 1

The standard short method of multiplication can be used when multiplying a decimal by a single digit. Children need plenty of practice with this before moving on to working with decimals.

The key to success with these is to place the answer in the correct columns and the best bet is to put the decimal point in first. Think of the decimal point as a fixed point, therefore the point in the answer should be immediately above the point in the question. Apart from that, these should prove to be straightforward.

This maths worksheet shows the method and then gives 12 questions to practice.

Multiplying decimals (pg 1)