5.1 is greater than 5.099, because the value of the 1 in 5.1 is more than the value of the 99 in 5.099.
The value of 1 in 5.1 is 0.1, while the value of the 99 in 5.099 is 0.099.
Since 0.1 is bigger than 0.099, then 5.1 is bigger than 5.099.
Also, 5.1 is greater than 5.099 because a bigger number on 5.1 (which is 1) is closer to the decimal point compared to 5.099 (1 is bigger than 0). the closer a decimal is to the decimal point the higher its value.