Graham,
If there are 700 line in total and 500 are on order A then fivesevenths of the lines are on order A. Fivesevenths ( ^{5}/_{7}) as a decimal fraction is 0.714 and hence the proportion of the lines that are on order A is 0.714. To express this as a percentage you need to multiply by 100 to get 71.4% of the lines are on order A.
Penny
