Addition is the process of finding the total or sum by combining two or more numbers.

Subtraction is the process of finding the difference between two numbers by taking one number away from another.

A whole number is a number without fractions; it is a non-negative integer (0, 1, 2, 3, ...).

A decimal is a fraction expressed in a special form, where the denominator is a power of ten, represented with a decimal point.

To add decimals, align the numbers by the decimal point and add as you would whole numbers, placing the decimal point in the sum.

To subtract decimals, align the numbers by the decimal point and subtract as you would whole numbers, placing the decimal point in the difference.

The sum of 4.2 and 7.98 is 12.18.