Question

$15x+17y=21$ and $17x+15y=11$ then. What is the value of $x+y$ ?

• A. $5$
• B. $4$
• C. $1$
• D. $0$

Answer 1

Answer: (C)

$1$

$15x+17y=21$ .....$\left(1\right)$

$17x+15y=11$ .....$\left(2\right)$

$17\times$eqn$\left(1\right)-15\times$ eqn$\left(2\right)$ gives

$255x+289y-255x-225y=357-165$

$\Rightarrow 64y=192$

$\Rightarrow y=\frac{192}{64}=3$

Substitute the value of $y=3$ in $\left(1\right)$ we get

$15x+17\times 3=21$

$\Rightarrow 15x=21-51=-30$

$\therefore x=\frac{-30}{15}=-2$

Hence $x=-2,y=3$

And $x+y=-2+3=1$