The mean of four nunbers is 70. The mean increases to 80 when a fifth number is added. What is the fifth number.

Respuesta :

4 number mean = 70
Each number = 70 = n
4n = 280
(280 + x) / 5 = 80
280 + x = 400
x = 120
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Double-Check
280 + 120 = 400
400 / 5 = 80