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A student has a mean score of 88 on five tests taken. What score must she obtain on her next test to have a mean (average) score of 80 on all six tests?

  • math -

    Mean score of tests :

    ( x1 + x2 + x3 + x4 + x5 ) / 5 = 88 Multiply both sides by 5

    x1 + x2 + x3 + x4 + x5 = 88 * 5

    x1 + x2 + x3 + x4 + x5 = 440


    Mean score of six tests :

    ( x1 + x2 + x3 + 4 + x5 + x6 ) / 6 = 80

    [ ( x1 + x2 + x3 + 4 + x5 ) + x6 ] / 6 = 80

    ( 440 + x6 ) / 6 = 80 Multiply both sides by 6

    440 + x6 = 80 * 6

    440 + x6 =480

    x6 = 480 - 440

    x6 = 60

  • math -

    ( x1 + x2 + x3 + x4 + x5 + x6 ) / 6 = 80

  • math -

    x6 = 480 - 440

    x6 = 40

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