A primary root grows from 5 cm to 19 cm in a week. Calculate the growth rate and relative growth rate over the period.
Lt = L0 + rt ... (i)
where Lt = length at time ‘t’ , L0 = length at time ‘zero’ , r = growth rate / elongation per unit time.
Here, Lt = 19 cm
L0 = 5 cm
t = 1 week
Putting these values in equation (i)
Relative growth rate = 
= 
Hence the growth rate is 14 cm per week while the relative growth rate is 280%.
1