Rob is a high school student taking both algebra and geometry. Last night he had 27 homework problems combined from the two classes, and he took a total of 90 minutes to do them. If each algebra problem took him 2 minutes and each geometry problem took him 5 minutes, how many algebra problems did he have for homework?
2
5
12
15

  15

Step-by-step explanation:

Let x represent the number of algebra problems. Then the number of geometry problems was 27-x and the total working time was ...

  2x +5(27 -x) = 90

  -3x = 90 -135 . . . . subtract 135

  x = -45/-3 = 15 . . . divide by -3

Rob had 15 algebra problems for homework.

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the answer is 31.27mph