Question

sol. (3) Let the distance of the destination from the starting point ( =x mathrm{km} ) Rate downstream ( =(10+4) mathrm{kmph}=14 mathrm{kmph} )
Rate upstream ( =(10-4) mathrm{kmph}=6 mathrm{kmph} )
According to the question.
( Rightarrow frac{x}{14}+frac{x}{6}=5 )
( Rightarrow frac{3 x+7 x}{42}=5 )
( Rightarrow 10 x=42 times 5 )
( Rightarrow x=frac{42 times 5}{10}=21 mathrm{km} )

# 3.2. A man goes downstream with a boat to some destination and returns upstream to his origi- nal place in 5 hours. If the speed of the boat in still water and the stream are 10 km/hr and 4 km/hr respectively, the distance of the destina- tion from the starting place is (1) 16 km (2) 18 km (3) 21 km (4) 25 km

Solution