\begin{align*}\dfrac{1}{5}x-\dfrac{1}{15}y&=4\\\\\dfrac{3}{7}x-ay&=b\end{align*}

In the system of equations above, a and b are constants. If the system has an infinite number of solutions, what is the value of b ?

A)
B)
C)
D)

 


 

Comments (2)

Maybe faster? Since “infinite solutions” means they are the same line, we can just set the 2 equations equal to each other, no? For my solution, I multiplied each term in first equation by 15 to get rid of fractions, multiplied each term in second equation by 7 to rid fractions, then set equations equal. You could then see that -7b must = -60, so set 7b = 60 and solve for b.

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