Question 950981
The difference in the two amounts is simple interest on the original principal for 7 months.:$2800-2668.75=$131.25 $131.25/7 mos=$18.75/mo
$18.75/mo*9 mo=$168.75  $2668.75-$168.75=$2500 
ANSWER 1: The original sum invested was $2500
CHECK:
$18.75/mo*16 mo=$300 $2800-$300=$2500 
PART 2: INTEREST RATE
($18.75/$2500)(100 %)=0.75%/mo ANSWER 2: The interest rate is 0.75% per month.