Year 5 Maths Handy Revision Guide (Autumn Term)

Year 5 Maths Handy Revision Guide (Autumn Term)

Multiplying by 10, 100 and 1000

When we multiply by 10 the number becomes 10 times bigger. The digits move one place to the left.

H

T

U

12 x 10

Th H T U 12 X 100

To multiply by 10 move each digit one decimal place to left and add zero as a place saver when needed. To multiply by 100 move each digit two decimal places left.

When we multiply by 100 the digits move 2 places to the left and so on.

TOP TIPS The easy way to multiply whole numbers by 10, 100, 1000 is to add zeroes. (X 10 add 1 zero) e g. 33 X 10 = 330 (X 100 add 2 zeroes) e.g. 41 X 100 = 4100 (X 1000 add 3 zeroes) e.g. 71 X 1000 = 71,000

For decimal numbers (which are not whole) hop the decimal point to the right always remembering we are making the number bigger. 1 place to the right for X 10 e.g 38.9 X 10 = 389 2 place to the right for X 100 e.g. 8.12 X 100 = 812 3 place to the right for X 1000 e.g. 9.13 X 1000 = 9130

Dividing by 10, 100 and 1000 When we divide by 10 the number becomes 10 times smaller. The digits move one place to the right.

When we divide by 100 the number becomes 100 times smaller. The digits move two places to the right,

H

T

U

Th H T U

130 ? 10

8800 ? 100

TOP TIPS The easiest way to divide whole numbers which end in zeroes is to take off the same number of zeroes as you are dividing by e.g. 3700 ? 100 = 37 (take off 2 zeroes) 770 ? 10 = 77 (take off 1 zero)

For numbers which do not end in zeroes the easiest way to hop the decimal point to the left always remembering we are making the number smaller.

1 place to the left for ? 10 e.g. 379 ? 10 = 37.9 2 places to the left for ? 100 e.g. 889 ? 100 = 8.89

Factors

The factors of a number are the numbers which divide exactly into it (`Fit' into it) without a remainder.

To find factors don't just guess by randomly thinking of numbers, work through the numbers in order.

Example: The factors of 16 are 1, 2, 4, 8 and 16

The pairs of factors of 12 are 1 x 12, 2 x 6, 3 x 4

Multiples A number adding onto itself again and again e.g. multiples of 2 would be 2, 4, 6, 8, 10, 12, 14 etc.

multiples of 5 would be 5, 10, 15, 20, 25, 30, 35 etc

TOP TIP Multiples are More , Factors Fit

Square Numbers and Square Roots

A number multiplied by itself is a square number. They are square numbers because they can be drawn in the shape of a square. The opposite of a square number is called a square root.

Squares

Square Roots

1? = 1 2? = 4 4? = 16 5? = 25 6? = 36 7? = 49 8? = 64 9? = 81 10? = 100

1 = 1 4 = 2 16 = 4 25 = 5 36 = 6 49 = 7 64 = 8 81 = 9 100 = 10

Cube Numbers and Cube Roots

A number multiplied by itself and then by itself again e.g. 2 X 2 X 2 is a cube number. The opposite of a cube number is called a cube root.

At Year 5 we only need to learn the first 3 cube numbers

Cube

Cube Roots

1? = 1 2? = 2 x 2 x 2 = 8 3? = 3 x 3 x 3 = 27

?1 = 1 ?8 = 2 ?27 = 3

Prime Numbers

A number which has only one pair of factors itself and 1 is a prime number. Nothing divides into a prime number apart from 1 and itself. The first prime number is 2. It is the only even prime number These are the first 10 prime numbers.

2, 3, 5, 7, 11, 13, 17, 19, 23, 29

Prime Factors

We find the prime factors of a number using a factor tree. For example find the prime factors of 12. Start with the number in the middle of the page. Write down a pair of factors as the first branches

12

6 2

If the number is prime leave it alone and put a circle round it (like a stop sign). If not write it as a pair of factors using more branches.

12

6 2

3 2

Continue until all the numbers at the end of the branches are prime numbers. The prime factors of 12 are all the numbers with circles around them So 12 = 2 x 2 x 3

Rounding

When we round to the nearest 10 we need to look at the units column to see if we need to round up or down Example: Number of people at Hall Grove School is 374, to the nearest 10 is 370.

When we round to the nearest 100 we need to look at the tens column to see if we need to round up or down

Example: Number of people at Hall Grove School is 374, to the nearest 100 is 400

When we round to the nearest 1000 we need to look at the hundreds column to see if we need to round up or down

Example: Number of people in Windlesham is 8374, to the nearest 1000 is 8000

Remember : If the number we are looking at is 5 or above we round up. Example: 285 to the nearest 10 is 290

Decimal numbers can be rounded to the nearest whole number, Example: 5.78 to the nearest whole number is 6 32.89 to the nearest whole number is 33 12.06 to the nearest whole number is 12

This is especially useful when we use money or measures such as length or mass ?2.76 to the nearest pound is ?3 4 m 35 cm can be rounded to 4 m, to the nearest metre

Negative Numbers Numbers don't just stop at zero. When you count backwards from zero, you go into negative numbers.

Positive numbers are more than zero. Negative numbers are less than zero. Use a number line to order negative numbers. For instance, it is easy to see that -2 is a higher number than -5 because it is further to the right on the number line.

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download