3 bottles contain 1.3l, 0.9l and 0.5l. Find the millilitres the mean average of these quantities

To find the mean average, you need to add up all the quantities and then divide by the number of quantities.

1.3l = 1300ml
0.9l = 900ml
0.5l = 500ml

Total = 1300ml + 900ml + 500ml = 2700ml

Now, divide the total by the number of quantities (3):

Mean average = 2700ml / 3 = 900ml

Therefore, the mean average of these quantities is 900 millilitres.