Answer: Interest rate can vary
Explanation: Based on the description of Greg's and Joyce's mortgage loan, the key term is the adjustable nature of the loan used to finance the mortgage. Being adjustable simply means not fixated. Hence, the interest on the loan is bound to change throughout the entire period of the loan. This type of mortgage loans are called ADJUSTABLE RATE MORTGAGE or FLOATING mortgage. The change in the interest rate applied on the outstanding balance of is usually at intervals which could be annually, semianually or monthly basis as the case may be.