Averages from Grouped Data Flashcards

All 6 cards in this deck

What is the modal class of a grouped frequency table?

The class interval with the highest frequency.

How do you find the midpoint of a class interval?

e.g. $10 \le t < 20$

Add the two end values and divide by 2.
$(10+20)\div2 = 15$

What are the steps to estimate the mean from a grouped frequency table?

e.g. $0<t\le10$ (frequency $3$), $10<t\le20$ (frequency $2$)

1. Find each midpoint: $5$ and $15$
2. Work out $\Sigma fx$: $5\times3+15\times2=45$
3. Divide by $\Sigma f$: $45\div5=9$

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

Because the exact data values are unknown, so midpoints are used to represent each class.

True or false? The modal class of a grouped frequency table is the class with the largest values.

False. It is the class with the highest frequency.

True or false? You can work out the exact range from a grouped frequency table.

False. You can only estimate it, since the largest and smallest actual values are not known.