Ex 3.6

Chapter 3 Class 10 Pair of Linear Equations in Two Variables
Serial order wise     This video is only available for Teachoo black users

Solve all your doubts with Teachoo Black (new monthly pack available now!)

### Transcript

Ex 3.6, 2 Formulate the following problems as a pair of equations, and hence find their solutions: (i) Ritu can row downstream 20 km in 2 hours, and upstream 4 km in 2 hours. Find her speed of rowing in still water & speed of the current. Let the speed of boat in still water be x km/hr & let the speed of current be y km/hr Now, Speed downstream = x + y Speed upstream = x – y Ritu can row 20 km downstream in 2 hours For downstream Distance = 20 km Time = 2 hours Speed = x + y We know that Speed = (𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 )/𝑇𝑖𝑚𝑒 x + y = 20/2 x + y = 10 Ritu can row 4 km upstream in 2 hours For upstream Distance = 4 km Time = 2 hours Speed = x – y We know that Speed = (𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 )/𝑇𝑖𝑚𝑒 x – y = 4/2 x – y = 2 Hence, our equations are x + y = 10 …(1) x – y = 2 …(2) From (1) x + y = 10 x = 10 – y Putting x = 10 – y in (2) x – y = 2 (10 – y) – y = 2 – 2y = 2 – 10 – 2y = −8 y = (−8)/(−2) y = 4 Putting y = 4 in (1) x + y = 10 x + 4 = 10 x = 10 – 4 x = 6 Thus, x = 6, y = 4 is the solution Hence Speed of boat in still water = x = 6 km/hr Speed of stream = y = 4 km/hr 