How fast was the battery charged? How long did it take the battery to be fully charged?

Question

A battery was charged. When the charging began, it was 23 percent full. After 30 minutes of charging, the battery was 89 percent full. 

Answer 1

r = rate of charging in %/min

 

t = time in minutes

 

r = (89 - 23)% / (30 min) = 2.2 %/min

 

q(t) = % charge as a function of time

 

q₀ = % of initial charge = 23%

 

q(t) = q₀ + rt

 

q(t) = 23 + 2.2t,

 

with t in minutes, q in %

 

Time to fully charge:

 

100 = 23 + 2.2t

 

t = (100 - 23)/2.2 min = 35 min