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How full was the battery when the charging began?

Mark charged a battery. Each minute, the percentage of the battery's capacity that was charged increased by 2.52.52, point, 5 percent. After 171717 minutes of charging, the battery was 61.561.561, point, 5 percent full.
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1 Answer

The equation of the line is y = Mx + b
 
 
 Changing the variables, 
   let y = E be the energy in the battery in terms of a percent
 
  let x = t, be the time in minutes.
 
The battery is at 61.5615% at 17 minutes, so (17, 61.5615)
The battery charges M = 2.525% every minute, which is the slope.
 
E = 2.525*t + B
 
61.5615 = 2.525*17 + B
 
B = 61.5615- 2.525*17
   = 18.6365
 
So the model is 
  E = 2.525*t + 18.6365
 
The intercept at t=0 when the charging began, there was B=18.6365%
 
The battery will be full at 100% when
  100 = 2.525*t + 18.6365
 
  t = (100 - 18.6365)/2.525 = 32.2231683
 
    32 minutes and 13.5 seconds