4) 162.75 / 31 = $5.25 per student

5) a) 13.52 + 26.05 + x = 71.85

So, x = $32.28

b) 13.52 / 30 = Approx. $0.45 per day for gas

26.05 / 30 = $0.87 per day for electricity

7) a) Assuming fortnight means 2 weeks, assuming 52 1/7 weeks in a year:

52  1/7  *  1294.82 = 67,330.64

b) 322.85/1294.82 = Approx. 25% in taxes.  So, Wendy would keep 75%.  So, 67,330.64 * 75% = $50,497.98

9) 424 + 586 + 489 + 386 + x = 3000

So, x = 3000 - 424 - 586 - 489 - 36 = 1115 km

10) 23 hrs, 56 min, 4 sec would be 23:56:04

9 hrs, 50 min, 30 sec would be 9:50:30

Subtracting the two, we have to borrow a minute from the first one.  So:

23:56:04 --> 23:55:64

So, 23:55:64 - 9:50:30 = 14:05:34, or 14 hours, 5 minutes, and 34 seconds.  You have to be careful of the subtracting from 60 seconds and 60 minutes on problems like this.  It doesn't occur here.

13) Various ways it can be done, all are similar.  There is no math formula you can follow.  Just plug in numbers until they work.  One way is:

4, 9, 2

3, 5, 7

8, 1, 6

14) Since the sequence of numbers are similar, only adding 2 to each, then if we were to add 2 to each number in #13, we would get 21, what we are looking for.  So:

6, 11, 4

5, 7, 9

10, 3, 8