Plan A: $480/year
Plan B: $250/6 months
One year = 12 months = 6 months x 2
So, if Plan B costs $250 every 6 months, you simply have to multiply 250 by 2 which equals:
250 x 2 = 500
In conclusion, Plan A is $480/year and Plan B is $500/year.
480 < 500 so Tammy is correct, Plan B costs more.