Represent the following pair of equations graphically and write the coordinates of points where the lines intersect y-axis :
x + 3y = 6
2x - 3y = 12
Let the constant expenditure be Rs. x
and consumption of wheat = y quintals
When rate per quintal = Rs. 250 Then,
Total expenditure = constant expenditure +
(consumption × rate per quintal)
Case I.
1000 = x + (y × 250)
⇒ 1000 = x + 250y
Case II. 980 = x + (y × 240)
⇒ 980 = x + 240y
Thus, we have following equations
x + 250y = 1000 ...(i)
x + 240y = 980 ...(ii)
From (i), we have
x = 1000 - 250y ...(iii)
Substituting this value in (ii), we get
(1000 - 250y) + 240y = 980
⇒ 1000 - 250y + 240y = 980
⇒ 1000 - 10y = 980
-10y = 980 - 1000
⇒ -10y = -20
⇒ y = 2
Substituting this value in (iii), we get
x = 1000 - 250 × 2
⇒ x = 1000 - 500
⇒ x = 500
Hence, total monthly expenses = Rs. 500
Now, total expenses when the price of wheat is Rs. 350 per quintal
= x + 350y
= 500 + 350 × 2
= 500 + 700
= Rs. 1200. Ans.