Interest issues are involved from primary school to middle school. Interest problems seen in primary schools are simple interest problems, while interest problems in junior high schools and senior high schools are generally compound interest calculation problems, and now bank deposits are compound interest calculation problems.

For example, the principal is A yuan (that is, A yuan has just been deposited), and the interest rate of each period is R (according to bank deposits, three months is 1, six months is 1, and two years, three years and five years is1); R is generally variable, and the range is generally 2%

1 Calculated according to the simple interest problem: after one deposit, the sum of principal and interest is a+ar; after two deposits, the principal of the second deposit is still A (the interest of the first deposit is not included in the principal), so the interest of the second deposit is still ar, the sum of principal and interest of the two deposits is a+2ar, the deposit term is N, and the sum of principal and interest after deposit is a+nar.

2 According to the compound interest problem: after the first period, the sum of principal and interest is a+ar=a( 1+r), which is deposited in two periods, and the principal of the second period is a( 1+r) (the interest of the first period is included in the principal), so the sum of principal and interest of the second period is A (1+R)+A.