Question

The speed of the boat in calm water is 30 km/h. A boat takes the same time to travel 10 km
upstream as it does to travel 15 km downstream. Find the speed of the river current.

The correct ans is 6km/h. But how?​

Answer 1

• $\small\sf{Let,\:the\:speed\:of\:the\:river\:be\:x\:km/hr.}$

${ }$

$\small\sf{\blue{⚘}}{\:Speed\:of\:boat\:in\:upstream\:(x\:+\:30)\:km/hr}$

$\small\sf{\blue{⚘}}{\:Speed\:of\:boat\:down\:stream\:=\:(30\:-\:x)\:km/hr}$

${ }$

$\small\sf{\bold{❥\:ATQ}}$

$\small\sf{:⟹}\:\sf\frac{10}{30\:-\:x}\:\small\sf{=}\:\sf\frac{15}{30\:+\:x}$

$\small\sf{:⟹\:300\:+\:10x\:=\:450\:-\:15x}$

$\small\sf{:⟹\:25x\:=\:750}$

$\small\sf{:⟹\:x\:=\:30}$

• $\sf{\bold{\purple{†}}}{\bold{\underline{\:Speed\:of\:the\:river\:current\:is\:\:km/hr.}}}$