Of federal taxpayers who itemize their deductions and have adjusted gross incomes between $35,000 and $50,000, the dollar amount of gifts to charity claimed on Schedule A is normally distributed with a mean of $549 and a standard deviation of $168.

a. What percentage of taxpayers with adjusted gross incomes between $35,000 and $50,000 will claim less than $400 in gifts to charity on Schedule A?

b. What percentage of taxpayers with adjusted gross incomes between $35,000 and $50,000 will claim between $500 and $600 in gifts to charity on Schedule A?

c. The IRS decides to audit any return for which the deduction for gifts exceeds that for 99% of those who itemize and have adjusted gross incomes of between $35,000 and $50,000. Above what dollar figure is a tax return automatically flagged according to this criterion?