Task: Question Answering
Input (English): Problem: the average weight of 20 persons sitting in a boat had some value . a new person added to them whose weight was 50 kg only . due to his arrival , the average weight of all the persons decreased by 5 kg . find the average weight of first 20 persons ? 
Options: a ) 55 , b ) 56 , c ) 57 , d ) 58 , e ) 59
Output (English): a