## Formulae Exercise

1. The cost of car repairs is given by the formula
C = 40h + p

where h = hours taken and p = cost of parts. a. Find the cost of repairs if a job takes 4 hours and the parts cost \$250.

b. Find the cost of repairs for a big job (see picture above!) lasting 16 hours with parts of \$1250.

2. Substitute the values given in the following formulae to find the value of the unknown variable. Make sure that the correct units are given.

 (a) find the velocity v, when d = 90 km and t = 3 hours (b) A = l w find the area A, when l = 10 cm and w = 6 cm (c) find the circumference C, when = 3.1 and r = 6 cm (d) find the volume V, when A = 20 cm2 and h = 6 cm (e) find the height h, when x = 4 m and y = 3 m

3. A group of 20 adults and children go to watch a basketball game at a stadium in Christchurch.

 There are 15 adults and 5 children. The admission charges are: Adults \$5 Children \$2 The formula for the cost of admission is C = 5a + 2b. Where a is the number of adults and b is the number of children.

Use the formula to find the cost for the group.

4. A jar of lollies contains x red lollies and y green lollies.

a. The red lollies cost 20 cents each, the green lollies cost 30 cents each and the jar costs \$3.
Write down a formula for the total cost of the jar of lollies in dollars.

b. If there are 100 red lollies and 150 green lollies, use the formula to find the total cost, in dollars, of the jar of llollies.