An herbalist finds that about 25% of plants sprout within 35 days, and that about 75% of

Question:

An herbalist finds that about 25% of plants sprout within 35 days, and that about 75% of plants sprout within 65 days.
(a) If the time of sprouting is modeled with a Weibull distribution, what parameter values would be appropriate?
(b) Use this model to estimate the time by which 90% of plants sprout.