Question

# What is the ratio between times taken by a train 240 m long to cross an electric pole and a bridge of 80 m length ?A.2 : 3B.3 : 4C.4 : 5D.5 : 6

Hint: At first the train needs to cross an electric pole and the distance travelled to cross a pole is the length of the train . Next the train needs to cross a bridge of 80 m , so the distance travelled by the train to cross the bridge is the sum of the length of the bridge and length of the train. The ratio of these two distances give the ratio of the time as distance is proportional to time.

Step 1:
In the first case the train has to cross an electric pole .
Given that the length of the train is 240 m long .
We know that the length of the train is equal to the distance travelled by the train to cross the electric pole.
Therefore the distance travelled by the train to cross the electric pole = 240 m
Step 2 :
In the second case the train has to cross a bridge of 80 m long
Given that the length of the train is 240 m and length of the train is 80 m
Therefore the distance travelled by the train to cross the bridge is the sum of the length of the train and length of the bridge.
The distance travelled by the train to cross the bridge = 240 + 80 = 320 m
Step 3 :
We know that distance is proportional to time
Hence the ratio of the distances is proportional to the ratio of the time asked.
The ratio is 240 : 320
Simplifying the ratio to bring it to its simplest form we get 3 : 4.

The correct option is B.

Note: In solving ratio problems we need to make sure that both the quantities are of the same units.
If one quantity is given in metres and another in centimetres then we need to convert both to either metres or centimetres