Answers

  • Brainly User
2016-07-03T21:59:50+08:00
[(a+7) + (a+3)]/2 = 3a + 9

[a + a + 7 + 3]/2 = 3a + 9

[2a + 10]/2 = 3a + 9

2a + 10 = (3a + 9) (2)

2a + 10 = 6a + 18

2a - 6a = 18 - 10

-4a = 8

-4a/4 = 8/-4

a = -2   ⇒   ANSWER

Check:

[-2 + 7 - 2 + 3]/2 = 3(-2) + 9

[-4+10]/2 = -6 + 9

6/2 = 3

3 = 3  (True)

The sequence: 5, 3, 1

a + 7 = -2 + 7 = 5

3a + 9 = 3(-2) + 6 = 3    (mean)

a + 3 = -2 + 3 = 1



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