I have attached a print screen of this question. Now I have solved the problem, but only with the help of the marks, scheme. Don't get me wrong, I didn't just look at the MS and assumed it was the right ans. I kind of of reverse engine the ans. My problem is with part b) It tells me to use the model to predict the number of years needed for the population of deer to increase from 800 to 1800. I highlighted predict for a reason, which I will explain in a bit. Now from the previous question I know that [itex]a=1.1776[/itex] so If I solve the equation in terms of a^t I get this [itex]a^t=36[/itex] now if I insert the value of a into this a take log1.177636=t, I get a value close to 22; I don't have the exact vale to hand, so I assumed when the question predict it wants me to round to the nearest whole number. Now my issue is that originally I sub the actual value of a into the original equation and obviously got the wrong ans. But my question is why do I have to wait until the last part of solving to insert the value of a. The only conclusion I have managed to come to is that because the question states the a is a constant the value will not change so I should not multiple through in the original equation because it would change the value of the constant. I would appreciate any sort of advice on how to do these types of questions, I have been looking at the definition of "constant" in math terms which is why I drew the conclusion of what I have said. Big thanks in advance p.s the sub script of "a" in the print screen equation is t.