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Math help from the Learning Centre

This guide provides useful resources for a wide variety of math topics. It is targeted at students enrolled in a math course or any other Centennial course that requires math knowledge and skills.

Decimal Notation

The dot represents a decimal point where place values are separated by what is to the left and right. To the right of the decimal points such as a tenth \(\frac{1}{10}\), a hundredth \(\frac{1}{100}\), and so on. 


Name the following numbers:

1) \(203.65\) = Two hundred three and sixty-five hundredths

2) \(2.008\) = Two and eight thousandths


Write out the following numbers:

1) One thousand twenty-two and three tenths = \(1022.3\)

2) Eighty thousand and eighty thousandths = \(80,000.080\)

Converting Between Fractions and Decimals

The decimal place value determines how to convert a decimal into a fraction.



ends at the thousandths place value. Therefore you put the number over 1000


Simplify the fraction


See video below for more examples, including mixed fractions and converting from fractions back to decimals.


Rounding Decimal Notation

To round to a certain place:

  1. Locate the digit in that place.
  2. Consider the next digit to the right.
  3. If the digit to the right is 5 or greater, round up; if the digit to the right is 4 or lower, keep digit the same. 

Example 1

Round \(0.084\) to the nearest tenth.


Locate the digit in the tenths place


Consider the next digit to the right, 8

Since 8 is greater than or equal to 5, round up.



Example 2

Round \(212.5604\) to the nearest hundredths


Locate the digit in the hundredths place


Consider the next digit to the right, 0

Since 0 is 4 or lower, keep digit the same.


Decimal Arithmetic Operations

Example 1

You bought 3 items: one for $4.50, one for $0.35 and one for $15.04. What was your total?


The total price is the sum of the prices of each individual item.


Example 2

The price of a jacket originally costing $80.89 was discounted by $15.49. What is the new price of the jacket?


We have to subtract the discount from the original price.

\[Original \; price - discount = 80.89-15.49 = $65.40\]

Example 3

Using the formula \(Interest = Principal \times rate \times time\), what is the interest earned on a principal of $1000 with an interest rate of \(4%\) over 5 years?


We need to multiply $1000 by 0.04 and 5 to get the total interest.

\[1000 \times 0.04 \times 5 = $200\]

The interest earned is $200.

Example 4

You paid $128.94 for 6 lamps. How much does each lamp cost?
Round to the nearest cent.



Each lamp costs $21.49.

Creative Commons License
Designed by Matthew Cheung. This work is licensed under a Creative Commons Attribution 4.0 International License.
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