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Mathematics

Solve for x and y :

y+75=2yx4+3x5\dfrac{y + 7}{5} = \dfrac{2y - x}{4} + 3x - 5

75x2+34y6=5y18\dfrac{7 - 5x}{2} + \dfrac{3 - 4y}{6} = 5y - 18

Linear Equations

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Answer

Simplifying first equation :

y+75=2yx4+3x5y+75=2yx+12x2044(y+7)=5(2y+11x20)4y+28=10y+55x10055x+10y4y=100+2855x+6y=12855x=1286yx=1286y55 …….(1)\Rightarrow \dfrac{y + 7}{5} = \dfrac{2y - x}{4} + 3x - 5 \\[1em] \Rightarrow \dfrac{y + 7}{5} = \dfrac{2y - x + 12x - 20}{4} \\[1em] \Rightarrow 4(y + 7) = 5(2y + 11x - 20) \\[1em] \Rightarrow 4y + 28 = 10y + 55x - 100 \\[1em] \Rightarrow 55x + 10y - 4y = 100 + 28 \\[1em] \Rightarrow 55x + 6y = 128 \\[1em] \Rightarrow 55x = 128 - 6y \\[1em] \Rightarrow x = \dfrac{128 - 6y}{55}\text{ …….(1)}

Simplifying second equation :

75x2+34y6=5y183(75x)+34y6=5y182115x+34y6=5y182415x4y=6(5y18)2415x4y=30y10815x+30y+4y=108+2415x+34y=132 ……(2).\Rightarrow \dfrac{7 - 5x}{2} + \dfrac{3 - 4y}{6} = 5y - 18 \\[1em] \Rightarrow \dfrac{3(7 - 5x) + 3 - 4y}{6} = 5y - 18 \\[1em] \Rightarrow \dfrac{21 - 15x + 3 - 4y}{6} = 5y - 18 \\[1em] \Rightarrow 24 - 15x - 4y = 6(5y - 18) \\[1em] \Rightarrow 24 - 15x - 4y = 30y - 108 \\[1em] \Rightarrow 15x + 30y + 4y = 108 + 24 \\[1em] \Rightarrow 15x + 34y = 132 \text{ ……(2)}.

Substituting value of x from equation (1) in (2), we get :

15×1286y55+34y=132311×(1286y)+34y=13238418y+374y11=13238418y+374y=1452384+356y=1452356y=1452384356y=1068y=1068356=3.\Rightarrow 15 \times \dfrac{128 - 6y}{55} + 34y = 132 \\[1em] \Rightarrow \dfrac{3}{11} \times (128 - 6y) + 34y = 132 \\[1em] \Rightarrow \dfrac{384 - 18y + 374y}{11} = 132 \\[1em] \Rightarrow 384 - 18y + 374y = 1452 \\[1em] \Rightarrow 384 + 356y = 1452 \\[1em] \Rightarrow 356y = 1452 - 384 \\[1em] \Rightarrow 356y = 1068 \\[1em] \Rightarrow y = \dfrac{1068}{356} = 3.

Substituting value of y in equation (1), we get :

x=1286×355=1281855=11055=2.\Rightarrow x = \dfrac{128 - 6 \times 3}{55} \\[1em] = \dfrac{128 - 18}{55}\\[1em] = \dfrac{110}{55} \\[1em] = 2.

Hence, x = 2 and y = 3.

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