What amount did Jean earn from the commission on her sales in the first half of 1988 ?
(1) In 1988 Jean's commission was 5 percent of the total amount of her sales.
(2) The amount of Jean's sales in the second half of 1988 averaged $10,000 per month more than in the first half.
you need to know the actual amount of sale
statement 1: obviously insuff
statement 2: jean could be averaging $1 per month in the first half, and $10001 per month in the second half
OR $1000000/month in the first half and $1010000 in the second half
Both statement still don't tell you how much her sales was. Furthermore, you don't know what her commission rate in the first half of the year was, it could be the same for the whole year or not.