The interior angles of a pentagon are (2x + 5)o, (x + 20)o, xo, (3x…

Mathematics WAEC 2009

The interior angles of a pentagon are (2x + 5)o, (x + 20)o, xo, (3x – 20)o and (x + 15)o. Find the value of x

  • 80o
  • 70o
  • 65o checkmark
  • 40o

The correct answer is: C

Explanation

(2x + 5)o + (xo + 20o) + x + (3x - 20)o + (x + 15)o = (n - 2) x 180

8n + 20 = (5 - 2) x 180

where n = 5(Pentagon)

8n + 20 = 3 x 180

8n + 20 = 540

8n = 540 - 20

8n = 520

x = 65o

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