Math problem (Level 2) : Three persons in a train (FF4)

Taro, Jiro and Hanako took a train for 1 hour and 12 minutes.
Since only one seat opened, they decided to sit down by turns.
Jiro stood for the double of the time Taro stood.
Hanako stood for a time of 3/2 times that of Taro.
How long minutes did Taro stand? 




Answer
32 minutes

Solution
Assuming the time Taro stood is 1, that of Jiro is 2 and that of Hanako is 1.5. 
The ratio of the time that three people stood is being 1 : 2 : 1.5 = 2 : 4 : 3. 

Because one seat opened, one person sat and two would stand. 
Total hour two persons stood is 72 minutes × 2 = 144 minutes. 

Therefore the time Taro stood was calculated by 144 × 2 / (2+4+3) which is proportional distribution of total time of 144 minutes. 
It comes to 32 minutes.