Substitution method From equation (1) , y = 3x - 40 Substituting in equation (2) 4x - 2 (3x - 40) = 50 4x - 6x + 80 = 50 - 2x = 50 - 80 = -30x = 30-- =152 Substitute the value of x in equation (1) 3(15) - y = 40 45 - y = 40y = 45 - 40 = 5\ Total number of questions = 15 + 5 = 20
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Use the elimination method to solve the example-9
Example-10. Mary told her daughter, "Seven years ago, I was seven times as old as you werethen. Also, three years from now, I shall be three times as old as you will be." Find the presentage of Mary and her daughter. Solution : Let Mary's present age be x years and her daughter's age be y years. Then, seven years ago Mary's age was x - 7 and daughter's age was y - 7. x - 7 = 7(y - 7) x - 7 = 7y - 49 x - 7y + 42 = 0 (1)Three years hence, Mary's age will be x + 3 and daughter's age will be y + 3. x + 3 = 3 (y + 3) x + 3 = 3y + 9 x - 3y - 6 = 0 (2) Elimination method Equation 1 x - 7y = - 42 Equation 2 x - 3y = 6 (-) (+) (-) same sign for x, so subtract. -4y = -48