Calculation of 'a' (P = a-bQ)

I had this exact problem too. I've never seen this kind of question in ANY of the revisions I did. I was totally lost!!

You can find a through the equation MC = MR to maximise profit MC is the total variable costs

Son: Please do not answer in this forum - it is the Ask the Tutor Forum, and you are not the tutor :-) (Also, what you have written is wrong - the question does not give the marginal cost, and it is not needed !!!)

jdeally: The lower the selling price, the higher will be the demand. Therefore maximum demand will occur when the selling price is zero. So putting it in the price demand equation: 0 = a - (0.0004 x 1,000,000) a = 400

Sir, I was unlucky not to realize this simple thing that price is 0 when demand is maximum, and I started calculaton in this way: I left "a" unknown, a-2bQ, b=0.0004, Q=1 mln. So, I mistakenly started solving as :a- 2*400=mc.After having found value of mc, I found "a".I know that my mistake is that 1 mln is not profit maximising quantity,such a silly mistake... My question is, provided that I show good calculation of MC, and logic of finding Price (if even at the very beginning my equation was wrong and that I arrived at wrong value of P), how do you think, will I gain marks for calculations and how many points you think they will give me? Thank you.

I have absolutely no idea! If it was in Sections A or B, then you either get 2 marks for getting it correct, or you get zero. Nobody looks at your workings. If it was in Section C, then you will surely get some marks.