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past x laps

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past x laps

by shibal » Thu Apr 23, 2009 5:11 pm
for the past x laps around the track, steven's avg time per lap was 51 seconds. If a lap of 39 seconds would reduce his avg time per lap to 49 sec, what is the value of x?

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by truplayer256 » Thu Apr 23, 2009 5:49 pm
If Steven's average time per lap for the past x laps was 51 seconds, then his total time for the x laps would be 51*x seconds. From the information given in the problem, we know that if Steven runs 39 seconds on a lap, his average will go from 51 to 49. We can set up an equation:

(51x+39)/x+1=49
51x+39=49x+49
2x=10
x=5
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