A boat goes 40 km upstream and 50 km downstream in 10 hours. It goes 15 km upstream in 25 km downstream in 4 hours. The speed of the current?

see full answer

Start JEE / NEET / Foundation preparation at rupees 99/day !!

21% of IItians & 23% of AIIMS delhi doctors are from Sri Chaitanya institute !!

An Intiative by Sri Chaitanya

answer is C.

(Unlock A.I Detailed Solution for FREE)

Ready to Test Your Skills?

Check your Performance Today with our Free Mock Test used by Toppers!

Take Free Test

Detailed Solution

Speed of the boat = x km/hr

Speed of the current = y km/hr

$\begin{array}{l} \frac{40}{x - y} + \frac{50}{x + y} = 10 \to (1) \\ \frac{15}{x - y} + \frac{25}{x + y} = 4 \to (2) \\ \frac{1}{x - y} = u, \frac{1}{x + y} = v \\ 40 u + 50 v = 10 \Rightarrow 40 u + 50 v = 10 \\ 15 u + 25 v = 4 - 30 u - 50 v = 8 \\ 10 u = 2 \\ u = \frac{1}{5} \Rightarrow v = \frac{1}{25} \\ u = \frac{1}{5} \Rightarrow \frac{1}{5} = \frac{1}{x - y} \\ x - y = 5 x - y = 5 \\ x + y = 25 15 - y = 5 \\ 2 x - 30 y = 10 \\ x = 15 \\ S p e e d o f c u r r e n t = (y) = 10 k m /hr \end{array}$

Watch 3-min video & get full concept clarity

hear from our champions

Result Producing online coaching for JEE/NEET of south India

Largest All India Test Series for JEE/NEET

Best Books for IIT JEE

Best Books for NEET

🔥 Start Your JEE/NEET Prep at Just ₹1999 / month - Limited Offer! Check Now!

Get Expert Academic Guidance – Connect with a Counselor Today!

Result Producing online coaching for JEE/NEET of south India

Largest All India Test Series for JEE/NEET

Best Books for IIT JEE

Best Books for NEET