92 Unit 3 Problem solving: basic skills
Summary
• We have seen that, for some problems,
the important data is given clearly and
unambiguously: the skill in finding the
correct solution is to use the given data in
the correct way.• We have learned that it can sometimes be
useful to work backwards from the answer
to identify what needs to be calculated.Answer required Information requiredData givenCalculation Solution3 A pancake stall sells sweet pancakes
and savoury pancakes. The savoury
pancakes can have three toppings (eggs,
ham, tomato) which may be used in any
combination. The sweet ones come with
orange, lemon or strawberry jam with
either ice cream or fresh cream. How many
combinations does the stall sell?
4 I am going to change my phone contract.
The monthly contract I am considering
costs $30 per month with 75 minutes of
free calls and 100 free text messages.
Additional calls cost 10¢ per minute and
additional text messages 10¢ each. An
alternative is ‘Pay as you go’ which has no
monthly charge but all calls cost 30¢ per
minute and texts cost 10¢ each.
I typically make 100 minutes of calls
and 60 text messages each month. Which
would be the better contract for me and by
how much?
Answers and comments are on page 317.1 A department store is having a sale. The
advertising hoarding for the sale is shown
below:30% off if the marked prices
total more than $100.
If you buy three items, you
get the least expensive free.This is a bit ambiguous. I don’t know
whether they give me the free item before
they calculate whether it is over $100, or
after. Suppose I buy three items at marked
prices of $40, $40 and $30. What could I
expect to pay under either interpretation?
2 Sylvia Okumbe is trying to break her
national record of 14 minutes 35 seconds
for running 5000 m ( 12 12 laps of the
track). Her average time per lap for the
first 5 laps is 1 minute 13 seconds. What
average lap time does she need for the
remaining 712 laps?End-of-chapter assignments