All Scholars – Weekly Brainteaser 22/02/2016

In a supermarket, the first 25 customers of the day purchased an average of two items each.

After a further 15 customers, the average number of items purchased by each customer rose to eight.

What was the average number of items purchased by the last 15 customers only?

Answers on paper, with full name and form to Mrs Wardle by Monday 29th February, break time.  Please feel free to place your answer under my door, or email if you are unable to find me.