To answer this question we will use the following formula for annual simple interest:
where P is the initial amount, r is the annual interest rate, and t is the time in years.
Now, if he invested $1000 in a 5.5% interest account, then after 1 year he will earn:
Since he invested the remaining ($4000) in a 5.75% interest account, he will earn:
Then, after one year he will have a total of $4230+$1055=$5285, therefore he will gain $285.
Answer: $285.