Last updated at Dec. 28, 2018 by Teachoo

Transcript

Ex 3.7, 1 The ages of two friends Ani and Biju differ by 3 years. Ani s father Dharam is twice as old as Ani and Biju is twice as old as his sister Cathy. The ages of Cathy and Dharam differ by 30 years. Find the ages of Ani and Biju. Let the Present age of Ani = x years and the present age of Biju = y years. Given that the ages of Ani and Biju differ by 3 x y = 3 Given that Ani s father Dharam is twice as old as Ani Present Age of Dharam = 2x And Biju is twice as old as Cathy Present age of Biju = 2 Present age of Cathy Present age of Cathy = ( )/2 Present age of Cathy = /2 years Also, The ages of Dharam and Cathy differ by 30 years 2x /2 = 30 (4 )/2 = 30 4x y = 60 Hence, equations are x y = 3 (1) 4x y = 60 (2) From equation (1) x y = 3 x = 3 + y Putting = 3 + y in equation (2) 4x y = 60 4 (3 + y) y = 60 12 + 4y y = 60 12 + 3y = 60 3y = 60 12 3y = 48 y = 48/3 y = 16 Putting y = 16 in equation (1) x y = 3 x = 3 + y x = 3 + 16 x = 19 Therefore, Present age of Ani = x = 19 years Present age of Biju = y = 16 years. Note: Here, we are given that Ages of Ani and Biju differ by 3 We have taken x – y = 3, But we can also take y − x = 3 So, our equations will be y − x = 3 …(1) 4x − y = 60 …(2) On solving, we get x = 21, y = 24 Thus, Present age of Ani = x = 21 years Present age of Biju = y = 24 years. So, our answers are both x = 19 and y = 16 And x = 21 and y = 24

About the Author

Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.