Slide15.JPG

Slide16.JPG

Slide17.JPG

Slide18.JPG

Slide19.JPG

Slide20.JPG

Slide21.JPG

  1. Chapter 3 Class 10 Pair of Linear Equations in Two Variables
  2. Serial order wise
Ask Download

Transcript

Ex 3.7, 4 (Introduction) The students of a class are made to stand in rows. If 3 students are extra in a row, there would be 1 row less. If 3 students are less in a row, there would be 2 rows more. Find the number of students in the class. Introduction Let 2 Students stand in 1 row and there are 10 rows in total Total the number of Students = Number of Students in 1 row × Number of rows = 2 × 10 = 20 Students We will use the formula Total number of Students = Number of Students in 1 row × Number of rows Ex 3.7, 4 The students of a class are made to stand in rows. If 3 students are extra in a row, there would be 1 row less. If 3 students are less in a row, there would be 2 rows more. Find the number of students in the class. Let number of students in 1 row = x and number of rows = y Then, Total number of Students = Number of Students in 1 row × Number of rows Total number of Students = xy If 3 Students are extra in a row, there would be 1 row less. Hence, If 3 Students are less in a row, there would be 2 row less. Hence, Number of students in 1 row = x + 3 Number of rows = y − 1 Now, Total Number of Students = Number of Students in 1 row × Number of rows = (x + 3) (y − 1) Putting number of Students = xy xy = (x + 3) (y − 1) (x + 3) (y − 1) = xy x (y − 1) + 3 (y − 1) = xy xy − x + 3y − 3 = xy − xy − x + 3y − 3 = 0 x − 3y + 3 = 0 Number of Students in 1 row = x − 3 Number of rows = y + 2 Now, Total Number of Students = Number of Students in 1 row × Number of rows = (x − 3) (y + 2) Putting number of Students = xy xy = (x − 3) (y + 2) (x − 3) (y + 2) = xy x (y + 2) − 3 (y + 2) = xy xy + 2x − 3y − 6 = xy 2x − 3y − 6 = xy − xy 2x − 3y − 6 = 0 Hence, equations are x − 3y + 3 = 0 …(2) 2x − 3y − 6 = 0 …(3) From equation (2) x − 3y + 3 = 0 x = 3y − 3 Putting x = 3y − 3 in equation (3) 2x − 3y − 6 = 0 2 (3y − 3) − 3y − 6 = 0 6y − 6 − 3y − 6 = 0 3y − 12 = 0 3y = 12 y = 12/3 y = 4 Putting y = 4 in equation (2) x − 3y + 3 = 0 x − (3 × 4) + 3 = 0 x − 12 + 3 = 0 x − 9 = 0 x = 9 Therefore, Number of Students in 1 row = x = 9 Number of rows = y = 4 Total Number of Students = Number of Students in 1 row × Number of rows = 9 × 4 = 36

About the Author

Davneet Singh's photo - Teacher, Computer Engineer, Marketer
Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 8 years. He provides courses for Maths and Science at Teachoo. You can check his NCERT Solutions from Class 6 to 12.
  • aaradhya kishor's image
    aaradhya kishor
    May 29, 2018, 1:19 p.m.
     Solve this by sustitution method.   
    Root7x root13y=9 and root5x root17y=0
    View answer
  • Sugan Kasana's image
    A man travel 370km partly bytrain and partly by car.if the cover 250km by train and test by car it take him 4hr but if he travel 130kmby train and restby car it take 18mins longer find the speed of car and that of train

    View answer