The Following Range-Checking Code Works but Is Somewhat Inefficient

The following range-checking code works but is somewhat inefficient.Explain why and show how to revise it to be more efficient.
if (saleAmount >= 1000)
commissionRate = 0.08;
else if (saleAmount >= 500)
commissionRate = 0.06;
else if (saleAmount <= 499)
commissionRate = 0.05;