<PRE><B>Question 1049625</B>
Let x = amount of time it takes the sister to complete route by herself
:
Sister = 1/x route per minute
Brother = 1/45 route per minute
Together = 1/20 route per minute
Put these together in an equation:
1/x + 1/45 = 1/20 multiply each term by 90x
90+2x = 4.5x
90 = 2.5x
x = 36
It takes the sister 36 minutes.</PRE>