One hundred million (100,000,000) divided by one thousand two hundred months (1,200) that is one hundred years (100 years)

One hundred million calculated for 1,200 months is a odd number of 99,999,996 to be a even number add 4.00 to 99,999,996 to equal 100,000,000

Calculate 
100,000,000 / 1,200 = 83,333.33

Calculate 
83,333.33 x 1,200 = 99,999,996

Calculate 
99,999,996 – 100,000,000 = 4.00

Calculate 
99,999,996 + 4.00 = 100,000,000

1,200 x 83,333.33 is 99,999,996
1 x 4.00
Calculate
99,999,996 + 4.00 is 100,000,000