# the speed of a boat in still water is 15 km / hr . it can go 30 km upstream and return downstream to the orginal point in 4 hours and 30 minutes . find the speed of the stream .

Given -

Speed of water = 15km/hr

Distance travelled upstream and downstream = 30 km

Let, speed of stream be x km/hr

So, time taken to travel 30km upstream = 30/15-x

and, time taken to travel 30km downstream = 30/15+x

Time taken to travel 30km upstream and 30km downstream = 4 hour 30 min or 9/2 hours

So, the equation formed will be

30/15-x + 30/15+x = 9/2

=> 30(1/15-x + 1/15+x) = 9/2

=> 1/15-x + 1/15+x = 9/2*30 = 3/20

=> (15+x+15-x)/225 - x2 = 3/20

=> 30/225-x2 = 3/20

=> 225-x2 = 30*20/3

=> 225-x2 = 200

=> x2 = 225-200

=> x2 = 25

=> x = 5

But, x = speed of stream

So, speed of the stream = 5 km/hr

Hope this helps!!

• 196
How 9/2*30 becomes 3/20 It should be 135
• -9
The given equation is 30(15+x+15-x)=9/2 So now Transfer 30 to LHS it becomes (9/2)/30 is nothing but 9/2*1/30=3/20 I hope this helped you !! 😊✌👍
• -7
Given - Speed of water = 15km/hr Distance travelled upstream and downstream = 30 km Let, speed of stream be x km/hr So, time taken to travel 30km upstream = 30/15-x and, time taken to travel 30km downstream = 30/15+x Time taken to travel 30km upstream and 30km downstream = 4 hour 30 min or 9/2 hours So, the equation formed will be 30/15-x + 30/15+x = 9/2 => 30(1/15-x + 1/15+x) = 9/2 => 1/15-x + 1/15+x = 9/2*30 = 3/20 => (15+x+15-x)/225 - x2 = 3/20 => 30/225-x2 = 3/20 => 225-x2 = 30*20/3 => 225-x2 = 200 => x2 = 225-200 => x2 = 25 => x = 5 But, x = speed of stream So, speed of the stream = 5 km/hr Hope this helps!!
• 2
Thank you sooo much
• -1
Given - Speed of water = 15km/hr Distance travelled upstream and downstream = 30 km Let, speed of stream be x km/hr So, time taken to travel 30km upstream = 30/15-x and, time taken to travel 30km downstream = 30/15+x Time taken to travel 30km upstream and 30km downstream = 4 hour 30 min or 9/2 hours So, the equation formed will be 30/15-x + 30/15+x = 9/2 => 30(1/15-x + 1/15+x) = 9/2 => 1/15-x + 1/15+x = 9/2*30 = 3/20 => (15+x+15-x)/225 - x2 = 3/20 => 30/225-x2 = 3/20 => 225-x2 = 30*20/3 => 225-x2 = 200 => x2 = 225-200 => x2 = 25 => x = 5 But, x = speed of stream So, speed of the stream = 5 km/hr
• 5
135
• -4
the answer is plus or minus 5

• 1
5 km / hr

• 1
5km /hr
• 1
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