I am the black child of a white father, a wingless bird, flying even to the clouds of heaven. I give birth to tears of mourning in pupils that meet me, even though there is no cause for grief, and at once on my birth I am dissolved into air. What am I?
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?