During the growth of a root of dicot the final length is 18cm after a period of 3 days. The growth of root in every 12 hours is 2cm. What is the initial length of root at time zero?

Increasing in length of root is an example for arithmetic growth. It can be estimated with the formula ${\mathrm{L}}_{\mathrm{t}}$ (length after time t) = ${\mathrm{L}}_0$ (initial length at time zero) + r(increase in length in unit time) t ( total period of growth). If we substitute the give values in the equation, then 18 cm = ${\mathrm{L}}_0 + 2\mathrm{X}6. {\mathrm{L}}_0$ = 18 – 12 = 6cm.