Question 243397
Three people run a mile. The first person runs the mile in seven minutes.
 The second person takes 5/4 as long as the first person. 
How many minutes did it take the third person to run the mile if the average for all three people is eight minutes? 
:
Let t = time of the 3rd person
:
Change 5/4 to 1.25
:
{{{(7 + 1.25(7) + t)/3}}} = 8
:
{{{(7 + 8.75 + t)/3}}} = 8
:
{{{(15.75 + t)/3}}} = 8
:
Multiply both sides by 3
15.75 + t = 24
:
t = 24 - 15.75
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t = 8.25 min is the 3rd person's time
:
:
Check solution
{{{(7 + 8.75 + 8.25)/3}}} = 8