Joseph and Mark have $230. Joseph and Kevin have $130. Mark had 3 times as much money as Kelvin. How much money does Kelvin have?

Step-by-step explanation:

Let's call Joseph "J", Mark "M", and Kevin "K" for ease. We need a system of equations to solve this, 3 equations for 3 unknowns. The first equation is

J + M = 230. The second equation is

J + K = 130. The third equation is

M = 3K. Sub that 3K into the first equation and get

J + 3K = 230. Now take th second equation and solve it for J:

J = 130 - K. Now sub 130 - K into the re-written first equation to get a whole new equation in terms of K only:

130 - K + 3K = 230 and

2K = 100 so

K = 50

Kevin has $50

the answer is c

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