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Math Help - Finite Math

  1. #1
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    Finite Math

    A student has an average of 92 after 3 tests. He scores 77 on the 4th test.

    What score would he need to make on the 5th test to have an average of

    90? Please show the formula used to get to the final answer. THANKS!!!!
    Last edited by Susan Campbell; June 5th 2008 at 09:15 PM. Reason: Forgot to include pertinent info.
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by Susan Campbell View Post
    A student has an average of 92 after 3 tests. He scores 77 on the 4th test.

    What score would he need to make on the 5th test to have an average of

    90? Please show the formula used to get to the final answer. THANKS!!!!
    You don't want a formula you need to be shown how to approach problems so that you can tackle ones that you have never seen before.

    If the mean after the 5-th test is 90 then:

    \frac{s_1+s_2+s_3+s_4+s_5}{5}=90

    where s_i is the score on the i-th test.

    You are told that s_4=77, you are also told that the mean of the first three tests is 92, so:

    \frac{s_1+s_2+s_3}{3}=92

    So:

    {s_1+s_2+s_3}=92\times 3=276

    Combining these we have:

    \frac{s_1+s_2+s_3+s_4+s_5}{5}=\frac{(s_1+s_2+s_3)+  s_4+s_5}{5}=\frac{276+77+s_5}{5}=90

    From which you can find the required s_5.

    RonL
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