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Dorris's average mark out of three tests was 82. Her last mark was 3/2 times her first mark. The middle mark was 86. What was the difference between Dorris's first and last marks?

Guest Apr 22, 2017
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Let her 1st mark =M, then:

 

M + 86 + 3/2M =3 x 82=246, solve for M

M = 64 - Her 1st mark

64 x 3/2 =96 - Her last mark, so that:

64 + 86 + 96 =246/3 =82 - Her average mark.

Guest Apr 22, 2017

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