A tank of water can be emptied by a pipe of diameter d in 20 minutes then how much time will needed to empty it by a pipe of diameter 2d. d व्यास वाले एक पाइप के द्वारा कोई पानी की टंकी 20 मिनट में खाली की जा सकती है तो 2d व्यास वाले पाइप को उसे खाली करने में कितना समय लगेगा ?

The flow rate through a pipe is proportional to its cross-sectional area, which depends on the square of the diameter (area = πd²/4). If the diameter doubles from d to 2d, the area becomes 4 times larger (since 2² = 4). With 4 times the flow rate, the time needed reduces to 1/4 of the original. Original time = 20 minutes, so new time = 20/4 = 5 minutes.