Problem Solving

1.A crew can row a certain course up the stream in 84 mins, they can row the same course downstream in 9 mins less than they can row it in still water. How long would they take to row down with the stream.

(a) 45 or 23 mins
(b) 63 or 12 mins
(c) 60 mins
(d) 19 mins



2. if a,b,c,d are in continued proportion then a-d/b-c >= x. what is the value of x.

(a) 2
(b) 3
(c) 1
(d) 0

harry_x1 wrote:1.A crew can row a certain course up the stream in 84 mins, they can row the same course downstream in 9 mins less than they can row it in still water. How long would they take to row down with the stream.

(a) 45 or 23 mins
(b) 63 or 12 mins
(c) 60 mins
(d) 19 mins

let the length of the course be ..d ... and let us assume d to be 252 ..

so according to the given information we have 2 equations ..

first.... 252/(b-s)= 84 ...
second .... 252/b-252/( b+s) = 9

... so from the first eqn we have b-s = 3 .. so b = s+3 ... subsitute this value of b in the second eqn and we have .. and we get a quadratic eqn for s from which we get 2 values for s .. 9,1/2 .. subsequently we have 2 values for b .. 12 and 7/2 ....

... now the time taken to row down the stream is given by 252(b+s) ... substituing the 2 values for s and b we get the possible answer as .. 63 and 12 . so the answer is b

harry_x1 wrote:2. if a,b,c,d are in continued proportion then a-d/b-c >= x. what is the value of x.

(a) 2
(b) 3
(c) 1
(d) 0

.. i am not sure about this one .. r u sure the question is right ..

... if a,b,c,d, are in continued proportion that means a/b = b/c = c/d ... now let the values of a,b,c,d be -1,2,-4,8 ... respectively .. in such a case ... we have (a-d)/(b-c)= ( -1-8)/(2-(-4)) = -9/6 = -1.5 .. which negates all the choices given .. so plz check the question again ...

PS ... post if any doubts ...

gabriel the answer to second question is 3