3.5 Finding methods of solution 97
3 From my holiday cottage by the sea I can
see two lighthouses. The southern flashes
regularly every 11 seconds. The northern
lighthouse, after its first flash, flashes
again after 3 and 7 seconds. The whole
cycle repeats every 17 seconds.
They have just flashed at exactly the
same time, the northern one having just
started the cycle described above.
When will they both flash again at
exactly the same time?
4 The 23 members of a reception class in a
school have done a survey of which cuddly
toys they own. Pandas and dogs are the
most popular, but 5 children have neither
a panda nor a dog. 12 have a panda and
13 have a dog. How many have both a dog
and a panda?Answers and comments are on pages 317–18.1 Aruna’s neck chain has broken into two
parts. She has lost the broken link and
is having it repaired by a jeweller who will
open one of the remaining links and use it
to rejoin the chain. The chain is made from
metal 2 mm thick and each of the broken
pieces has a fitting at the end used for
closing the chain which each adds 1 cm to
the total length.One of the broken pieces is 34.2 cm long
and has 10 more links than the other,
which is 26.2 cm long. Excluding the
fittings at the ends, how many links will
there be in the complete chain?
2 The distance from Los Angeles to Mumbai
is 14,000 km. Flights take 22 hours,
whilst the return flight from Mumbai to
Los Angeles takes only 17 hours because
of the direction of the prevailing wind.
Assuming the aeroplane would fly the
same speed in both directions in still air,
what is the average wind velocity?End-of-chapter assignments