উত্তর সিলেক্ট করলে সঠিক ও ভুল দেখাবে।
ব্যাখ্যা ও সঠিক সমাধান
উত্তর:
25
Let the total distance be D.
Distance travelled at 50 mph = 75% of D = 0.75D
Time taken = 0.75D/50 hour
Distance travelled at S mph = 25% of D = 0.25D
Time taken = 0.25D/S hour
Now, 0.75D/50 + 0.25D/S = D/40
or, 0.75/50 + 0.25/S = 1/40 [ dividing both sides by D]
or, 0.25/S = 1/40 - 0.75/50 = (5 - 4×0.75)/200 = 1/100
or, S = 0.25×100 = 25 mph