9. A computer company gives a discount of 10% on a new piece of software. If it makes a profit of 4%, what percent does the marked price exceed the cost price?

Let m represent the marked price, s represent the price at which the product is sold, p represent the profit amount, and c represent the cost price. We have these relationships.
  m(1 - 10%) = s
  s - p = c
  p/s = 4%
We want to find the ratio of m to c.
We can solve the third equation for p and substitute that into the second equation.
  p = 4%*s
  s - (4%*s) = c
  s(1 - 4%) = c
  s = c/(1 - 4%)
Now, we can substitute this into the first equation and solve for m/c
  m(1 - 10%) = c/(1 - 4%)
  m/c(1 - 10%) = 1/(1 - 4%)
  m/c = 1/((1 - 4%)(1 - 10%))
  m/c = 1/(.96*.90) = 1/.864
  m/c ≈ 1.157407...
We are actually interested in
  (m-c)/c = m/c - 1 ≈ .157407...
Multiplying this by 100%, we get
The marked price exceeded the cost price by 15.7407...%.