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Linear Equations in One Variable

SAT Math· difficulty 3/5

John is 4 years older than his sister. Five years ago, he was twice her age. How old is John now?

  • A

    17

  • B

    20

  • C

    9

  • D

    13

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Explanation

J=S+4J = S + 4. J−5=2(S−5)J - 5 = 2(S - 5) → S+4−5=2S−10S + 4 - 5 = 2S - 10 → S=9S = 9, J=13J = 13.

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