 Hello and welcome to the session. In this session we discussed the following question that says a boat goes 20 kilometers downstream in 2 hours and 4 kilometers upstream in 2 hours. Find first the speed of boat in still water, second speed of the current. Let's move on to the solution now. First of all we assume let the speed of boat in still water be equal to x kilometers per hour and let the speed of current be equal to y kilometers per hour for downstream distance covered is equal to 20 kilometers and time taken is equal to 2 hours. So the speed downstream is equal to distance upon time that is 20 upon 2 and 2 10 times is 20 so this is equal to 10 kilometers per hour is the speed downstream. Now next for upstream distance covered is equal to 4 kilometers and the time taken is 2 hours. So now speed upstream is equal to distance covered that is 4 upon the time taken that is 2. And 2 2 times is 4 so this is equal to 2 kilometers per hour is the speed upstream. Now that we have assumed that the speed of the boat in still water to be x kilometer per hour and speed of the current to be y kilometer per hour. So we have speed downstream would be given by x plus y kilometer per hour therefore we have that x plus y is equal to 10. Since we had find out speed downstream to be 10 kilometer per hour so let this be equation 1. Also the speed upstream would be given as x minus y kilometer per hour and we had found out the speed upstream to be 2 kilometers per hour therefore x minus y is equal to 2. Let this be equation 2. Now that we need to solve the two equations 1 and 2 so now adding equations 1 and 2 we get x plus y plus x minus y equal to 10 plus 2 y cancels with minus y and we have 2x is equal to 12 dividing both sides. So by 2 we get x equal to 6. Now we will find the value of y by substituting the value of x in 1 so substituting the value of x in 1 we get 6 plus y is equal to 10 that is y is equal to 10 minus 1. So this is minus 6 or you can say y is equal to 4. So thus we have got the values for x and y. We had assumed x to be the speed of the boat in still water and y to be the speed of current. So therefore we have speed of the boat in still water to be 6 kilometer per hour and speed of the current to be 4 kilometer per hour. So this is our final answer. This completes the session. Hope you have understood the solution of this question.