They may be ellipsis which represent repeating digits.
The number 1231 as a decimal is simply 1231. This is because whole numbers are already in decimal form, with no fractional or decimal parts. Decimals are a way to represent numbers that are not whole, such as fractions or numbers with decimal points. In this case, 1231 is a whole number and is already in decimal form.
110.101 is already a decimal number. Unless that is intended to be two binary numbers with a decimal point between them for some reason. (decimal points are not used to represent fractional numbers in the binary system).
There should be no points after the decimal point.
87.656 87.66
Decimal points aren't positive or negative. Decimals can be either.
The fourth place behind the decimal point is 10/1000s and the fifth place behind the decimal point is 100/1000s.
Put the numbers in a column with the decimal points aligned. Add the numbers ignoring the decimal points. Insert the decimal point in the answer exactly below the column of decimal points in the numbers being added (summands).
Write the numbers in a column so that all the decimal points are one below the other. Put a decimal point in the answers underneath the coumn of decimal points. Then add the numbers ignoring the decimal points.
A number with two decimal points cannot be a decimal number.
Unlike addition, there is no need to line up the decimal points. Just multiply ignoring the decimal points. When you are done, move the decimal point of the result to the left equal to the number of digits after the decimal point for both multiplicands.
In the context of numerical values, 9.00 and 9.0 are considered the same because they both represent the number 9 with two decimal places. The extra zero after the decimal point in 9.00 is insignificant and does not change the value of the number. Therefore, mathematically speaking, 9.00 and 9.0 are equivalent representations of the same numerical value.
A decimal number can't have two decimal points in it