Hello, subject, here is my answer: * stands for multiplication sign and ≈ stands for power.

1, the sum of principal and interest =100000 * (1+6%) 5 ≈1000000 *1.338226 ≈13382.26 yuan;

2. Principal =10000 ÷ (1+5%) 3 ≈ 8638.38 yuan;

3. Sum of principal and interest = {20000 * (1+5%)+20000 * (1+5%)+20000} * (1+5%) ... The formula is too long, in short, it starts from the second year.

Step by step: the sum of principal and interest at the end of the first year = 20000 * (1+5%) = 21000 yuan.

At the end of the second year, the sum of principal and interest = 41000 * (1+5%) = 43,050 yuan.

At the end of the third year, the sum of principal and interest =63050*( 1+5%)=66202.5 yuan.

Total principal and interest at the end of the fourth year = 86,202.5 * (1+5%) = 90512.63 yuan.

Total principal and interest at the end of the fifth year =110512.63 * (1+5%) =16038.26 yuan.

So the final sum of principal and interest is 1 16038.26 yuan.