Wonderful world of Decimals

WONDERFUL WORLD OF DECIMALS

What is a decimal number?

A decimal is a part of a whole.

•Think about money

1 dollar and 4 dimes

•1.40$

Whole

Part of the whole

On a number line

1 4 0

Converting from fraction to Decimal• THERE ARE 2 WAYS• 1) You can write the fraction with a denominator that is a

power of 10.• (10,100,1000….)

Denominator is the bottom number of a fraction• Ex

• =

Step 2• Than move your decimal place one spot to the left, because the 10 has 1 zero.

• 6.

0 .6

More examples

How many decimal points will I move to the left?

245.

Look at money again.

•It takes 10 dimes to make 1 dollar.

So 1 dime is 1 tenth of the whole

It takes 100 pennies to make 1 dollar

A penny is one hundredth of a dollar

Second way

•Divide the numerator by the denominator.

• 7÷16• =0.4375

Express the following mixed fraction as a decimal

• 2 =2. a decimal•2÷3 =0.66•2.66

Homework• Pg 90#15,16,17

• Pg 91# 18,19,20

Comparing decimal numbers• If 2 decimal numbers have different wholes • Ex.• 4.56 and 7.89

• The one with the larger whole is bigger.

Comparing decimal numbers• If the 2 numbers have the same whole but different

decimal numbers.

• 6.54 and 6.43

• The one with the larger tenth digit is bigger

Adding and subtracting decimals• Example : 235.7 +18.276• 1) Write digits with the same position under each other

and line up the decimal point.• 235.7• + 18.276

• 2) Add or (subtract) the numbers ignoring the decimal point.

• 235.7• + 18.276

Adding and subtracting decimals• 3) Place the decimal point directly under the decimal of

the other numbers.• • 2 3 5 .7• + 1 8 .2 7 6

• 2 5 3. 976

Homework

Pg 94#1-5

Word Problem• You are going shopping for groceries and you want to

save as much money as possible. Here are the prices at 2 stores: Item Loblaws Super C

Milk 3.59$ a litre 3.55$ a litre

Bread 4.39$ 3.99$

Eggs 5.19$ for 12 4.39 $ for 12

Yogart 2.99$ for 2 3.45$ for 6

Which Grocery store would give you the best deal overall and how much would it cost?

Pg 95• #7-11

Multiplication and division of decimals• 1) When multiplying by a power of ten (10,100,1000…)

Move the decimal one place to the right for every zero

Example: 3.45 X100 3.45 =345.00

Multplication with decimal numbers

003.45 =.00345

Move the decimal one place to the Left for every zero.

Multiplication• For all other numbers,• 1) Multiply them as if they were not decimal numbers.

• 35.18• X 4.7• 24 626• + 1 40 720• 1 65 346• 2) Count the number of decimal places in the 2 numbers• we have 3.• 3) Put the decimal place in the result so it is same as the

total of the 2 numbers.

Homework• Pg 96• ALL• Pg 97 #3 & 4