\f25. You initially have saved $50. Each month you add $10 more to your savings account. Write an explicit formula to model the amount you have saved after n months.20. Which expression can be used to find the number of permutations of n distinct objects taken r at a time? (n-r)!r! ( n -r ) ! C. n!r! d. none of these13. In a recursive formula, each succeeding term is formulated from the firstterm of the sequence. a. True b. False