Averages from Grouped Data Flashcards

All 5 cards in this deck

What are the steps to work out an estimate for the mean from a grouped frequency table?

e.g. $0 < t \le 10$ (frequency 3), $10 < t \le 20$ (frequency 2)

1. Find the midpoint of each class: $5$ and $15$
2. $\sum fx = 5 \times 3 + 15 \times 2 = 45$
3. Divide by $\sum f = 5$: estimated mean $= 9$

How do you find the midpoint of a class interval?

e.g. $20 < t \le 30$

Add the two end values and divide by 2.

$(20 + 30) \div 2 = 25$

What is the modal class of a grouped frequency table?

The class interval with the highest frequency.

True or false? The median of grouped data is the midpoint of the middle class in the table.

False. You must use the frequencies to find which class contains the middle value.

Why is the mean found from a grouped frequency table only an estimate?

The exact data values are not known, so each value is assumed to be the midpoint of its class.