Subject: General Aptitude · Chapter: Boats and Streams · Exam: · Marks: · Difficulty:
A boat goes 30 km upstream and 44 km downstream in 10 hours. In 13 hours, it can go 40 km upstream and 55 km downstream. The speed of the boat in still water is (I.I.F.T., 2008)
(a)3 km/hr
(b)4 km/hr
(c)8 km/hr
(d)None of these
Answer
Answer (as printed):
Explanation
Let rate upstream = $x$ km/hr and rate downstream = $y$ km/hr. Then, $\frac{40}{x}+\frac{55}{y}=13$ ...(i) and $\frac{30}{x}+\frac{44}{y}=10$ ...(ii). Multiplying (ii) by 4 and (i) by 3 and subtracting, we get $y=11$. Substituting $y=11$ in (i), we get: $x=5$. $\therefore$ Rate in still water $=\frac{1}{2}(11+5)$ kmph $=8$ kmph. Rate of current $=\frac{1}{2}(11-5)$ kmph $=3$ kmph.
Explanation as extracted from the printed page; notation may be imperfect.