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john is 3 times as old as susan. Mark is 5 years younger than john the sum of their ages is 30. how old is susan

Respuesta :

Answer:

Susan is 5 years old

Step-by-step explanation:

Make a system of equations based on the info:

J=3S

M=J-5

J+M+S=30

Since we have the value of J, plug it in to either equation:

M=3S-5

Same deal with M:

3S+3S-5+S=30

7S-5=30

7S=35

S=5

So Susan is 5 years old

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