maths F.4!!!!quick!!today need

(a)
Cost of one fish = total cost/number of fish = $120/p
The unit price at which Miss Lam sold the goldfish = 120/P + 1

(b)
Selling price per fish * Total number of fish sold – Total cost of fish = profit
(120/P + 1) * (P -4) – 120 = 24
(120/P + 1) * (P -4) = 144
(120 + P)/P * (P -4) = 144
(120 + P) * (P -4) = 144P
(P + 120) * (P -4) = 144P
4(P+30)* (P-4) =144P
(P+30)* (P-4) =36P
P^2 +26P – 120 = 36P
P^2 -10P – 120 = 0
(p – 40)(p + 30) = 0
p = 40 or p = -30 (reject negative number)

p = 40


2011-07-27 20:41:39 補充：
* is multiplication sign (x)

Godfrey:
(P + 120) * (P -4) = 144P
4(P+30)* (P-4) =144P (this step is wrong)

(P +120) cannot be equal to 4(P+30)

2011-07-27 22:43:24 補充：
Godgrey:

Maybe it is much simpler than you thought.
Let me try it with a different interpretation of the question.

2011-07-27 23:00:27 補充：
(1) 120/(p-4) + 1

(2) {120/(p-4) + 1} * (p -4) = 120 + 24

p = 28

(it is a different interpretation of the question)

2011-07-28 09:42:19 補充：
According to Godfrey's interpretation:

(P + 120) * (P - 4) = 144P
P^2 -4P + 120P - 480 - 144P = 0
P^2 - 28P - 480 = 0 (find m,n where m+n = -28; m*n=-480)
(P - 40) * (P + 12) = 0 (m=-40; n=12)
if (P - 40) = 0 ; P = 40
if (P +12) = 0 ; P = -12 (dicarded)

P = 40