Question

John believes that the amount of sleep he gets the night before a test and his score on that test are inversely related. On his first exam, he got eight hours of sleep and scored 70 on the exam. To the nearest tenth, how many hours does john believe he must sleep the night before his second exam so that the average of his two exam scores is an 80?.

Answer 1

John will need to sleep for 10.3 hours before  his second exam so that the

average of his two exam scores is an 80.

We were given

8 hours of sleep = 70

To get average of 80

70+ x = 80

  2

Cross multiply:

70+x = 160

x= 160-70

 = 90.

If  8 hours of sleep = 70

       x hours of sleep = 90

Cross multiply

8× 90 = 70 × x

720 = 70x

x = 720/70

x  = 10.2857

    ≈ 10.3 hours of sleep

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