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
<u>70+ x</u> = 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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