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Minimize z = 6x + 21y subject to x + 2y ≥ 3, x + 4y ≥ 4, 3x + y ≥ 3, x ≥ 0, y ≥ 0 show that the minimum value of z occurs at more than two points - Mathematics and Statistics

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प्रश्न

Minimize z = 6x + 21y subject to x + 2y ≥ 3, x + 4y ≥ 4, 3x + y ≥ 3, x ≥ 0, y ≥ 0 show that the minimum value of z occurs at more than two points

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उत्तर

To draw the feasible region, construct table as follows:

Inequality x + 2y ≥ 3 x + 4y ≥ 4 3x + y ≥ 3
Corresponding equation (of line) x + 2y = 3 x + 4y = 4 3x + y = 3
Intersection of line with X-axis (3, 0) (4, 0) (1, 0)
Intersection of line with Y-axis `(0, 3/2)` (0, 1) (0, 3)
Region Non-origin side Non-origin side Non-origin side

x ≥ 0, y ≥ 0 represent 1st quadrant.

Shaded portion XABCDY is the feasible region, whose vertices are A(4, 0), B, C and D(0, 3).

B is the point of intersection of the lines x + 4y = 4 and x + 2y = 3.

Solving the above equations, we get

x = 2, y = `1/2`

∴ B ≡ `(2, 1/2)`

C is the point of intersection of the lines x + 2y = 3 and 3x + y = 3.

Solving the above equations, we get

x = `3/5`, y = `6/5`

∴ C ≡ `(3/5, 6/5)`

Here, the objective function is Z = 6x + 21y

∴ Z at A(4, 0) = 6(4) + 21(0) = 24

Z at B`(2, 1/2) = 6(2) + 21(1/2)`

= `12 + 21/2`

= `45/2`

= 22.5

Z at C`(3/5, 6/5) = 6(3/5) + 21(6/5)`

= `18/5 + 126/5`

= `144/5`

= 28.8

Z at D(0, 3) = 6(0) + 21(3) = 63

∴ Z has minimum value 22.5 at B`(2, 1/2)`.

∴ Z has minimum value 22.5 when x = 2 and y = 0.5.

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Linear Programming Problem (L.P.P.)
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