Respuesta :

She should get 84 in her fifth test to have an average of 80

(75 + 81 + 77 + 83 + x)/5 = 80

(316 + x)/5 = 80

[(316 + x)/5] (5) = 80(5)

316 - 316 + x = 400

316 + x = 400 - 316

x = 84

jcherry99

Remark

You set this up as (75 + 81 + 77 + 83 + x)/5 = 80      Combine the left

(316 + x)/5 = 80                                                           Multiply by 5

316 + x = 80 * 5

316 + x = 400                                                              Subtract 316

316 - 316 + x = 400 - 316

x =  84  <<<< Answer

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