Mean of Frequency Tables

1. At a party, thirty people have an age of 30, forty have an age of 40 and fifty an age of fifty. What is their average age?

2. In a hardware shop, there are 30 spanners costing £6, 55 hacksaws costings £9 and 10 soldering irons costings £20. What is the average cost per item?

3. Using this frequency table, find the average height of a turnip.

Height (to nearest cm)

6cm 7cm 8cm 9cm 10cm

Frequency:

3 8 12 4 1