HSC Together Year 12 Maths Standard: Standard Deviation and the '65-95-99.7' Rule

#### Maths Standard

• Simultaneous Linear Equations
• Non-linear Relationships
• Non-Right Angled Trigonometry
• Rates and Ratios
• Investments and Loans
• Annuities
• Bivariate Data Analysis
• The Normal Distribution
• Network Concepts
• Critical Path Analysis
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# Standard Deviation and the ’65-95-99.7′ Rule

### What is standard deviation and the ’65-95-99.7′ rule?

Standard deviation is a measure of how spread out numbers are. The percentage of data that lies within a certain number of deviations is always the same. This is where the ’65-95-99.7′ rule comes in. If a set of data is normally distributed, we know that 68% of the data lies one standard deviation from the mean, 95% lies within the two standard deviations from the mean, and 99.7% lies within the three standard deviations from the mean. The following video introduces normal distribution, standard deviation and the 68-95-99.7 rule in HSC Standard Math.

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