**Category 15 Example 1 Question 1** - no calculation required

Total annual cost = annual membership + cost of p classes in a year = 25 + 20p

**Category 15 Example 1 Question 2** - mental math

Cost of 5 classes is 20 x 5 = 100. Hence, total annual cost = 25 + 100 = 125

**Category 15 Example 2** - mental math

Total books = existing books + 4 books per week for 7 weeks = 38 + 28 = 66

**Category 16 Example 1** - no calculation required

Total earnings = h hours at $15 per hour + c cakes at $2.50 each = 15h + 2.5c

**Category 17 Example 1** - no calculation required

The given equation can be interpreted as

total population in t years after 1998 = starting population in 1998 + average increase in population per year after 1998 for t years.

Hence, 130 is the average increase in population per year after 1998 for t years.

**Category 17 Example 2 Question 1 **- no calculation required

The given equation can be interpreted as

tusk size in m months after one year of birth = tusk size at one year + average increase in tusk size per month after one year of birth for m months.

**Category 17 Example 2 Question 2 **- no calculation required

For tusk size to increase by 1, 0.5583m must be equal to 1. Hence, m is the reciprocal of 0.5583 = 1/0.5583.

**Category 18 Example 1** - no calculation required

Total bushes = x + y = 12

Total cost = cost of x bushes at $35 each + cost of y bushes at $55 each --> 520 = 35x + 55 y

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