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Linear Equations in One Variable

SAT Math· difficulty 5/5

A jar contains red and blue marbles in the ratio 3:73:7. After 2020 red marbles are added, the ratio becomes 5:75:7. How many blue marbles are in the jar?

  • A

    105

  • B

    70

    check_circle
  • C

    35

  • D

    140

Explanation

Let red =3k= 3k, blue =7k= 7k. After: 3k+207k=57\frac{3k + 20}{7k} = \frac{5}{7}, so 7(3k+20)=35k7(3k + 20) = 35k, giving 140=14k140 = 14k and k=10k = 10. Blue =70= 70.

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