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.
There should be no points after the decimal point.
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).
87.656 87.66
Decimal points aren't positive or negative. Decimals can be either.
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).
The fourth place behind the decimal point is 10/1000s and the fifth place behind the decimal point is 100/1000s.
A number with two decimal points cannot be a decimal number.
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.
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.
Mapmakers use scale to represent distances between points on a map.
A decimal number can't have two decimal points in it