Formulate the following problems as a pair of equations, and hence find their solutions:
(i) Ritu can row downstream 20 km in 2 hours, and upstream 4 km in 2 hours. Find her speed of rowing in still water and the speed of the current.
(ii) 2 women and 5 men can together finish an embroidery work in 4 days, while 3 women and 6 men can finish it in 3 days. Find the time taken by 1 woman alone to finish the work, and also that taken by 1 man alone.
(iii) Roohi travels 300 km to her home partly by train and partly by bus. She takes 4 hours if she travels 60 km by train and remaining by bus. If she travels 100 km by train and the remaining by bus, she takes 10 minutes longer. Find the speed of the train and the bus separately.
(i) Let the speed of Ritu in still water and the speed of stream be x km/h and y km/h respectively.
Speed of Ritu while rowing
Upstream = (x-y) km/h
Downstream = (x+y) km/h
According to question,
2(x+y) = 20
= x+y = 10............(1)
2(x-y) = 4
= x-y = 2 ............(2)
Adding equation (1) and (2),
we obtain
2x = 12 = x = 6
Putting this in equation (1),
we obtain y = 4
Hence, Ritu's speed in still water is 6 km/h and the speed of the current is 4 km/h. (ii)Let the number of days taken by a woman and a man be x and y respectively.
Therefore, work done by a woman in 1 day = 
Work done by a man in 1 day = 
According to the question,
Putting 
in these equations,
we obtain
= 8p + 20q = 1
= 9p + 18q = 1
By cross-multiplication, we obtain
x = 18, y = 36
Hence, number of days taken by a woman = 18 Number of days taken by a man = 36
(iii) Let the speed of train and bus be u km/h and v km/h respectively.
According to the given information,
Putting 
in these equations, we obtain
60p+240q = 4 ......(3)
100p+200q = 
600p+1200q = 25 ....(4)
Multiplying equation (3) by 10, we obtain
600p+2400q = 40 ....(5)
Subtracting equation (4) from (5), we obtain
1200q = 15
..... (6)
Substituting in equation (3), we obtain
60p+3 = 4
60p = 1
u = 60km/h and v = 80km/h
Hence, speed of train = 60 km/h
Speed of bus = 80 km/h