Cindy paddles her kayak upstream at x kilometers per hour, and then returns downstream the same distance at n kilometers per hour. How many kilometers upstream did she travel if she spent a total of p hours for the round trip? Choose the correct choice from the following answers
A) mnp  B) mn/p  C) (x + n)/p  D) xnp/(x + n)  E) px/n- pn/x
let t1 and t2 be the time taken to row upstream and downstream respectively   now,   t1=distance/speed=d/x   similarly,   t2=d/n (as same distance has to be rowed)   also,   t1+t2=p   therefore,   p=(d/x)+(d/n)   =d(x+n)/xn   d=pxn/(x+n)=xnp/(x + n)
<result>D</result>
Cindy paddles her kayak upstream at x kilometers per hour, and then returns downstream the same distance at n kilometers per hour. How many kilometers upstream did she travel if she spent a total of p hours for the round trip?