Mai is mailing packages. Each small package costs her $2.50 to send. Each large package costs her $3.20. How much will
it cost her to send 3 small packages and 1 large package?
The cost to send 3 small packages is 3 * $2.50 = $<<3*2.5=7.50>>7.50.
The cost to send 1 large package is 1 * $3.20 = $<<1*3.2=3.20>>3.20.
Thus, the total cost is $7.50 + $3.20 = $<<7.50+3.20=10.70>>10.70. Answer: \boxed{10.70}.