As math

The area of each bar represents how many runners landed between those times. That is your 'frequency'.
The x axis is the time ranges. That is your 'group width'.
The y-axis is your frequency density. It's calculated by Frequency of runners / Group width = Frequency density
So if I had 4 runners (frequency) land a time between 55 mins and 65 mins that is a range of 10 mins(group width). My frequency density would be 0.4. On a graph the bar would have a width of 10 and a height of 0.4

So question 13
Frequency Density = 0.5 (y axis)
Group width = 12 (x axis difference between 78.5 and 90.5)
Frequency of runners / Group width = Frequency density
Frequency of runners / 12 = 0.5
Frequency of runners =0.5 x 12 = 6

Thanks!!

Any hep on other questions

The area of each bar represents how many runners landed between those times. That is your 'frequency'.
The x axis is the time ranges. That is your 'group width'.
The y-axis is your frequency density. It's calculated by Frequency of runners / Group width = Frequency density
So if I had 4 runners (frequency) land a time between 55 mins and 65 mins that is a range of 10 mins(group width). My frequency density would be 0.4. On a graph the bar would have a width of 10 and a height of 0.4

So question 13

Post what you've tried

I tried to differentiate couldnt see where cos came from