In common use, a decimal refers to part of a whole number. The numbers to the left of a decimal point represent whole numbers, and each number to the right of a decimal point represents a fractional part of a power of one-tenth. For instance: The decimal value 1.24 indicates 1 whole unit, 2 tenths, and 4 hundredths (commonly described as 24 hundredths).
To estimate is to find an approximate answer that is reasonable or makes sense given the problem.
Rounding is reducing the number of non-zero digits in a number while keeping the overall value of the number similar.
Learn to add and subtract decimals with and without rounding