A grouped data set has the following frequency distribution. The mean of the data is 40. Which one of the following equations can be used to calculate the missing frequency p?
Class interval: 30–40 40–50 50–60
Frequency: 10 p 6
a) 16+p350+45p=40
b) 10+p680+45p=40
c) 16+p760+50p=40
d) 16+p350+45p+330=40