question_answer

  A person rowing a boat at the rate of 5km/hour in still water, take thrice as much time in going 40 km upstream as in going 40 km downstream. Find the speed of the stream. OR In a competitive examination, one mark is awarded for each correct answer while  mark is deducted for each wrong answer. Jayanti answered 120 questions and got 90 marks. How many questions did she answer correctly?

Answer:

  Let speed of the stream be x km/hr Given speed of boat = 5 km/hr speed of boat in going upstream = (5 - x) km/hr speed of boat in going downstream = (5 + x) km/hr Now, time taken in going 40 km upstream This taken is going 40 km downstream According to question:  speed of stream = 2-5 km/hr OR Let the number of correct answers be x and number of wrong answers be y Mark awarded for each correct answer Mark awarded for x correct answers   Also, mark deducted for each wrong answer    Mark deducted for y wrong answers   According to question                        ...(1) and                                                                ...(2) On adding (1) and (2), we get  number of correct answers given by Jyanti = 100