On a river, Q is the mid-point b/w two points P and R on the same bank of the river. A boat can go from P to Q and back in 12 hours, and form P to R in 16 hours 40 min. How long would it take to go from R to P?

7\(\frac{1}{3}\) hrs

P_________ Q___________ R

        ↓

  P to Q 

  Q to P = 12 hrs    ---- (i)

This is the same time to go from Q to R and bacl, since distance is same = 12

Time to go from P to Q = Q to R  

total = 16 hr 40 min

time from P to Q = 8 hr 20 min

From eq (i) 

time taken from Q to P = 12 hr - 8 hr 20 min

                                   = 3 hr 40 min

Time taken to go from R to P = 2 x (3 hr 40 min)

                                           = 7 hr 20 min or 7\(\frac{1}{3}\) hrs