Statistics - Cumulative frequency - Standard deviation

When finding the positions of the quartiles FROM A CUMULATIVE FREQUENCY CURVE, you use the following formulae

• $\frac{N+1}{4};\ \frac{N+1}{2}\ and\ \frac{3\left(N+1\right)}{4}$

• $\frac{N}{4};\ \frac{N}{2}\ and\ \frac{3N}{4}$

The standard deviation is

• a dispersion parameter

• the square root of the variance

• the sum of the product of the midpoint and the frequency

• measuring how far away the individual numbers are from the mean

The frequency table shows the masses of 50 cats. The cumulative frequency table gives you the following values:

• 4; 12; 17; 10; 7

• 4; 16; 37; 67 ; 131

• 4;16; 33; 43; 50

The cumulative frequency graph gives information about the times it took boys to complete a puzzle. Use the graph to find the total number of boys who completed the puzzle.

• 40

• 60

• 10

The cumulative frequency graph gives information about the times it took boys to complete a puzzle. Use the graph to find an estimate for the median time.

• 35

• 33

• 13

• 18

The cumulative frequency graph gives information about the times it took boys to complete a puzzle. Use the graph to find an estimate for the quartiles.

• Lower quartile: 10 seconds

  Upper quartile: 30 seconds

• Lower quartile: 30 seconds

  Upper quartile: 40 seconds

• Lower quartile: 16 seconds

  Upper quartile: 45 seconds

• Lower quartile: 20 seconds

  Upper quartile: 50 seconds

The table below shows you informations about masses of cabbages. Choose the right calculations for finding an estimate for the mean and standard deviation

• 
  

  $\overline{x}=4.5$ $\sigma=\sqrt{2.45-4.5^2}$
  

• $\overline{x}=0.35$ $\sigma=\sqrt{\frac{2.45}{13}-0.35}$

• $\overline{x}=\frac{4.5}{13}\ \ \ \ \ \ \ \sigma=\sqrt{\frac{2.45}{13}-0.35^2}$

• $\overline{x}=\ 0.35\ \ \ \ \ \ \ \sigma=\sqrt{\frac{2.45}{13}}-0.35^2$