A, B and C can complete a work separately
in 24, 36 and 48 days respectively. They
started together but C left after 2 days of
start and A left 3 days before the completion
of work. In how many days will the work be
completed ?

Two trains 105 metres and 90 metres
long, run at the speeds of 45 km/hr
and 72 km/hr respectively, in opposite
directions. The time which they take to
cross each other, is –

Total distance to be covered
= 105 + 90 = 195 m
Relative speed = (45 + 72) km/hr
= 117 km/hr
= (117 x $5\over 18$)m/s
=
$65\over2$
m/s
So, time required to cross each other
= 195 $2\over 65$
= 6 sec

Two trains, each of length 125 metre, are
running in parallel tracks in opposite
directions. One train is running at a speed
65 km/hour and they cross each other in
6 seconds. The speed of the other train is –

Distance to be covered = 125 × 2 = 250 m
Time taken to cross each other = 6 sec
Relative speed =
($250\over 6$)
m/s
=
($250\over 6$ x $18\over 5$)
km/hr
= 150 km/hr
The speed of first train = 65 km/hr
The speed of second train = (150 – 65) km/hr
= 85 km/hr

Two candle of the same height are lighted
at the same time. The first is consumed in
3 hours and the second in 1 hour. Assuming
that each candidate burnished a constant
rate. In how many hours after being lighted,
the ratio between the first and second
candle becomes 2 : 1?

A motor-boat goes 2 km up-stream in a
stream flowing at 3 km per hr and returns
downst ream to the st art i ng point i n
30 minutes. Find the speed of the motorboat in still water.

Each edge of a regular tetrahedron is 3 cm,
then its volume is –
A.9$\sqrt2\over4$ $cm^3$
B.27$\sqrt3$ $cm^3$
C.4$\sqrt2\over9$ $cm^3$
D.9$\sqrt3$ $cm^3$