Percentage problems. Please Help

Arjun spends $15 of his monthly allowance on a new CD album and another 40% of what’s left on action figures. If he still has $9 remaining, how much is his total monthly allowance?

Let the amount left with Arjun after the CD purchase be x
Then the amount spent on action figures = 0.4x and the remaining amount is 0.6x
But, the remaining amount = $9

0.6x = 9
x = $15
Total monthly allowance = [spoiler]15 + x = 15 + 15 = $30[/spoiler]

a) $ 21
b) $ 24
c) $ 27
d) $ 30
e) $ 33

Dan has five times as many seashells as Paul, and eight more than Andrew. When Dan gives away 40% of his shells, Paul and Andrew agree to split those shells up evenly, giving Andrew twice as many as Paul. How many shells did Dan start with?

I feel this isn't complete. Do you mind letting me know if this is a correct question ?

At a computer store, 25% desktop computers are black, while the remaining desktop computers are beige. If 75% of the computers in the store are laptop computers (all of which are black), and the store sells only desktop and laptop computers, what percentage of the store's computers are black?

This question can be solved in 2 seconds flat. We know that the % of laptop(all black) is 75%. So the percentage of ALL black computers should be greater than 75%. Answer choice E is the only one that is greater than 75%.

For the benefit of problem solvers using conventional method.

Let the total number of computer be X, Then
The number of Laptop computers = 0.75X(All black)
The number of Desktop computers = 0.25X
The number of black desktop computers = 0.25*0.25*X
Total number of Black computers = Total number of Black laptop computers + Total number of Black Desktop computers = 0.75X+0.0625X = 0.8125X = 81.25%

Yes I am Very Sure this is the Correct Problem. Can you how can solve it. I also I appricate your help on the other previouse problems and thanks on your fast response.

neelgandham wrote:Dan has five times as many seashells as Paul, and eight more than Andrew. When Dan gives away 40% of his shells, Paul and Andrew agree to split those shells up evenly, giving Andrew twice as many as Paul. How many shells did Dan start with?

I feel this isn't complete. Do you mind letting me know if this is a correct question ?