有两道GMAT数学不会，请大牛们指导下。

stonesugar

If a and b are positive integers such that a – b and
are both even integers, which of the following must be an odd integer?

A a/2    B b/2   C a+b/2  D a+2/2   E b+2/2


Before being simplified, the instructions for computing income tax in country R were to add 2 percent of one's annual income to the average of 100 units of country R's currency and 1 percent of one's annual income. Which of the following represents the simplified formula for computing the income tax, in Country R's currency, for a person in the country whose income is I?

A 50+I/200   B 50+3I/100      C 50+I/40    D 100+I/500    E 100+3I/100
A a/2    B b/2   C a+b/2  D a+2/2   E b+2/2


Before being simplified, the instructions for computing income tax in country R were to add 2 percent of one's annual income to the average of 100 units of country R's currency and 1 percent of one's annual income. Which of the following represents the simplified formula for computing the income tax, in Country R's currency, for a person in the country whose income is I?

A 50+I/200   B 50+3I/100      C 50+I/40    D 100+I/500    E 100+3I/100

DeliciaAn

第3道转自这里：https://www.manhattanprep.com/gmat/forums/post11728.html
DaveGill:
2% of income (I) = (2/100)I

1% of income (I) = (1/100)I
100 units of R's currency = 100
Average of 100 units of R's currency and 1% of I = [100+(1/100)I]/2

Average added to 2% of I = (2/100)I+[50+(1/200)I]

and simplify to get:

50 + (I/40)

Answer is C.