1.   A surprising number of systems have neither of these.

2.   But among those students a considerable number have great difficulty with the university course.

3.   Can a negative number have a square root?

4.   French telephone numbers have six digits.

5.   Number three has a quite different style of roundel and, to me it looks as if the tail stripe colours are reversed!

6.   A growing number of households have at least one computer.

7.   In some areas it was reported that large numbers of troops had ben deployed to restore order.

8.   A number of factors have to be considered when determining the overall efficiency of a process and expected yield is only one of them.

9.   In pursuing a solution to the energy problem, a number of factors have to be taken into consideration.