August, 2009 | Maths Blog

Mental Arithmetic: Add 29, 39, 49 to any 2-digit number

Here we continue with our mental arithmetic series on addition by looking at adding 29, 39 and 49 to 2-digit numbers. Make sure that your child is confident with adding 9 before going on to these. Once again the process is the same: add the nearest whole ten and then subtract 1. Once this has been mastered similar techniques can be used to add 2-digit numbers that have 8 in the units, subtracting two rather than one, which makes adding any 2-digit numbers fairly straightforward!

This page, and many others, can be found in our Year 4 maths worksheets under Knowing Number Facts.

Add 29, 39, 49 to any 2-digit numbers

Coming Soon: Mental arithmetic and time.

The emphasis is on mental arithmetic next week. We continue with our mental arithmetic series on addition by looking at adding 29, 39 and 49 to 2-digit numbers. Also there is a tricky page on adding decimal fractions mentally, suitable for Year 5.

We also have our second in a series of time worksheets, looking at how long it is between two times which are at least one hour apart, using both digital and analogue clock faces.It is often useful to make jottings with these types of question, whether you count on the hours or the minutes first.

Talking of time, how the summer holiday seems to have flown by and it is only a couple of weeks before its back to school.

Year 5 maths worksheet: Adding decimal fractions mentally

$add-decimal-fractions-mentally-1$ This page is all about using mental strategies to add decimal fractions. Before attempting this children should be able to add two 2-digit whole numbers in their heads and have a good understanding of place value.

The mental process of adding 2.4 and 3.7 is almost the same as adding 24 and 37; in fact many people just ignore the decimal to work the answer out and then insert it at the end. Again, it is perfectly normal to add the units first and then the tenths, which is the opposite of doing it on paper.

The second half of the page looks at adding tenths and hundredths. A good way to look at this is to think of it as money ie adding pence and writing the answer as pounds (but without the sign!)

Add decimal fractions mentally (pg 1)

Resource of the Week: times tables number search

Looking for something to get the brain going again towards the end of the summer holiday? We have some great resources in our Puzzles section, including this one which is a number search using the 3 times table.

All of the 3 times table up to 10 can be found somewhere in the number search, either across or down, but it is not as easy as it looks as there are plenty of ‘red herrings’.

This is just one of quite a large selection of puzzles which MathSphere has given us for the site.

Enjoy the rest of the holiday!

3x table number search

Time: Finding lengths of time in minutes 1

Reading clock faces is a tricky subject for many children, especially as they see time displayed digitally more now than ever before.

This page looks at finding lengths of time under an hour by comparing two clock faces.

There are several stages of development with this and children should be able to count up in fives confidently before starting this exercise.

At first children will probably go round the clock face counting in fives. later they might well move in 30 minute or 15 minute blocks.

Finding lengths of time, reading clock faces (pg 1)

Standard written addition of 4-digits

Addition of two 4-digit numbers is usually done on paper, using the following standard method:

The method is to add the units first, put the units in the answer, and ‘carry’ the ten into the tens column. Then add the tens and continue in the same way into the hundreds and finally the thousands.

A clearer explanation is available on the first page of the worksheets, together with a page of questions, but briefly:

Looking at 5687 + 2546 the steps are:

Step 1: add the units

7 + 6 = 13

Put the 3 in the units below the question.
Then place the one ten below the answer in the tens column.

Step 2: add the tens
8 (tens) + 4 (tens) + 1 (ten) = 13 (tens)
Place the 3 (tens) in the tens column and the 1(hundred) in the hundreds column below the answer.

Step 3: add the hundreds
6 (hundreds) + 5 (hundreds) + 1 (hundred) = 12 (hundreds)
Place the 2 (hundreds) in the hundreds column and the 1(thousand) in the thousands column below the answer.

Note: there may not always be tens, hundreds or thousands to carry.

Step 4: add the thousands
5 (thousands) + 2 (thousands) + 1 (thousand) = 8 (thousands)
Place the 8 (thousands) in the thousands column.
Answer: 8233

Standard addition of 4-digits (pg 1)

Coming soon: Written addition, time and mental arithmetic

Next week we will have an excellent maths worksheet showing how to do standard written addition with 4-digit numbers. Also there will be a page on finding lengths of time using both analogue and digital displays. Time is often a stumbling block for many children, especially when asked to find how long it is between two times.
There will also be mental arithmetic for Year 5 children on adding decimal fractions – by no means easy! Great practice over the holiday at keeping those mental arithmetic skills razor sharp!

Maths Worksheet: Add 19 to any 2-digit Number

By year 4 children should be comfortable with 2-digit addition ‘in their heads’. This maths worksheet on adding 19 to any 2-digit number will show whether they are confident and quick with their mental methods.

There are usually two processes involved when adding 19. It is often best done by adding twenty and subtracting one, although some children may well add ten and then add 9. This is easier and quicker than writing the sum down in columns and adding up using the standard method.

Add 19 to any 2-digit number

Resource of the Week: Year 5 Probability

This week I am highlighting our probability worksheets for Year 5.

Probability is one of the least understood of maths concepts, especially with young children.

By year 5 children are expected to be able to say whether events are impossible , unlikely , likely or certain.

They should also be able to say which events have an even chance of happening (such as tossing a coin and getting a head), but they should be careful not to say that if there are two possibilities, they are equally likely. For example, there are two possibilities – I might buy a new Jaguar today or I might not. Unfortunately, these two events are not equally likely.

Another example of this is if I choose a number between 1 and 5. Is the number I choose a prime number? As there are three prime numbers between 1 and 5 (2, 3 and 5) and two numbers that are not, there is not an even chance that I will choose a prime number; rather there is a 3 in 5 chance, or 60% chance.

Year 5 probability pages

Subtraction of money

This is another in our series of worksheets covering the four rules. Children should be competent with the standard written method of subtraction before moving onto subtracting decimals. Money is an excellent way to show how decimals work and it is important to ensure that there are two numbers after the decimal point. Another key point, of course, is to make sure the columns are correctly in line and that a decimal point is included in the answer. Make sure that questions 9 to 15 are written out in the correct format: vertically rather than horizontally.

Standard money subtraction (p1)