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Learn in your speed, with individual attention - Teachoo Maths 1-on-1 Class


Transcript

Example 5 Aftab tells his daughter, “Seven years ago, I was seven times as old as you were then. Also, three years from now, I shall be three times as old as you will be.” (Isn’t this interesting?) Solve by the method of substitution.. Let the Current age of Aftab be x years. & let Current age of Aftab’s daughter be y years. Given that “Seven years ago, I was seven times as old as you were then” Seven years ago, Age of Aftab = x − 7 Age of Aftab’s daughter = y − 7 Aftab was seven times as old as Aftab’s daughter (x – 7) = 7(y – 7) (x – 7) = 7y – 49 x – 7y = 7 − 49 x – 7y = −42 Also, “three years from now, I shall be three times as old as you will be “ Three years later, Age of Aftab = x + 3 Age of Aftab’s daughter = y + 3 Aftab will be three times as Aftab’s daughter (x + 3) = 3(y + 3) (x + 3) = 3y + 9 x – 3y = 9 − 3 x – 3y = 6 So, our equations are x – 7y = −42 ...(1) x – 3y = 6 …(2) From (1) x – 7y = −42 x = 7y – 42 Putting value of x in (2) x – 3y = 6 (7y – 42) – 3y = 6 7y − 3y = 6 + 42 4y = 48 y = 48/4 y = 12 Putting y = 12 in equation (1) x – 7y = −42 x – 7(12) = −42 x − 84 = −42 x = −42 + 84 x = 42 So, x = 42, y = 12 is the solution of the equations Hence, Aftab’s age = x = 42 years His daughter’s age = y = 12 years

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.