On a mathematical calculation problem Bank interest calculation question: withdraw 5000 yuan, and the daily interest is 0.05% [for example, one day is 2.5 yuan, and the next day is (5000 + 2.5) * 0.0005]. Ask 31 days, how much is the interest? Again, if I return 100 yuan every month for 31 days, how many months can I repay all the money? Similarly, the remaining 100 yuan is still calculated according to the daily interest of 0.05%!

In fact, this problem can be solved by using the high school's equal ratio sequence
After 31 days, the total principal and interest is 5000 * (1 + 0.0005) ^ 31
(1 + 0.0005) ^ 31 is an equal ratio sequence with the first term of 1 and the common ratio of 1 + 0.0005. Just use the summation formula of the equal ratio sequence

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