Percentages

Answer : D

Amount = 10000 x (1 + 12%/12)^24

Note that 12% is the annual interest rate.
If the amount is compounded monthly, it should be divided by 12. (12 months in a year)
If the amount is compounded quarterly, it should be divided by 4.  (4 quarters in a year)

Note that there are 24 months in two years. Thus, the power should be 24.

Answer : A

Note that  B < C < A.
A is 30% greater than B à A = 1.3B
B is 30% less than C à B = 0.7C
Therefore, A = 1.3B = 1.3 x 0.7C = 0.91C which is 9% less than C.

Answer : C

Let $x be the marked price.
After 10% discount, the selling price = $0.9x
Profit percentage = (selling price - cost price) / cost price x 100%
20% =  $(0.9x - 19800) / $19800 x 100%
Solving it, we get x = 26400

Answer : E

Selling price of shop A = $0.9P
Selling price of shop B = $0.85Q
Therefore, 0.9P = 0.85Q
We get Q = 18P/17

Answer : A

Total cost = $30 + $70 = $100
Selling price of the first car = $30 x 1.2 = $36
Selling price of the second car = $70 x 0.9 = $63
Total amount he gets = $36 + $63 = $99
Percentage change = (new - old) / old x 100%
Therefore, percentage change = $(99-100)  / 100 x 100$ = -1%
Negative represents loss.

Answer : B

Let $x be the original hourly pay.
Original daily income = $8x
New hourly pay = $0.75x
New daily income = $7.5x
Percentage change = $(7.5x - 8x) / (8x) x 100% = -6.25%

Actually, you can assign any value for x. For instance, you may set x = 1 and get the same answer.