A bacterial population’s rate of increase, in millions of cells per hour, was recorded at the beginning of each 1-hour interval for the first 6 hours as shown below.
Time t (h): 0 1 2 3 4 5 6
Rate r(t) (millions/h): 2 3 4 5 6 7 8
If the total increase in population is estimated by multiplying each recorded rate by the length of its interval, will this estimate be an underestimate or an overestimate of the actual increase? Explain briefly.