The task is to generate the correct answer for a given math problem.

Q: Problem: a train passes a station platform in 30 sec and a man standing on the platform in 20 sec . if the speed of the train is 54 km / hr . what is the length of the platform ?

A: 60 
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Q: Problem: if a speaks the truth 40 % of the times , b speaks the truth 80 % of the times . what is the probability that at least one will tell the truth

A: 0.12
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Q: Problem: 120 kg of an alloy a is mixed with 180 kg of alloy b . if alloy a has lead and tin in the ratio 2 : 3 and alloy b has tin and copper in the ratio 3 : 5 , then the amount of tin in the new alloy is ?

A:
139.5 kg
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