Defenition: Adding and subtracting decimals, Write the decimals so that the decimal points line up vertically. Add or subtract as whole numbers. Place the decimal point in the sum or difference so that it lines up vertically with the decimal points in the problem. Multiplying decimals, Multiply the decimals as though they are whole numbers. The decimal point in the product is placed so that the number of decimal places in the product is equal to the sum of the number decimal places in the factors. Dividing by a decimal number, If the divisor is not a whole number, before we divide we need to move the decimal point to the right until the divisor is a whole number. Then we have to place the decimal point in the quotient directly above the decimal point in the dividend and then divide as with whole numbers. Calculation: \(\displaystyle{70}={y}\ -\ {22.81}\) Add 22.81 on both sides, \(\displaystyle{70}\ +\ {22.81}={y}\ -\ {22.81}\ +\ {22.81}\)

\(\displaystyle{70}\ +\ {22.81}\) 22.81 has 2 decimal place value. But 70 has no decimal place value. Add 0s after the decimal point of 70 The number becomes, 70.00 \(\displaystyle{70.00}\ +\ {22.81}\) Based on the definition, \(\begin{equation} \frac{\begin{array}[b]{r} 70.00\\ +\ 22.81 \end{array} }{ 92.81 } \end{equation}\)

\(\displaystyle{70.00}\ +\ {22.81}={92.81}\)

\(\displaystyle{70}\ +\ {22.81}={92.81}\)

\(\displaystyle-{21.81}\ +\ {22.81}\) Based on the definition, \(\begin{equation} \frac{\begin{array}[b]{r} -22.81\\ +\ 22.81 \end{array} }{ +00.00 } \end{equation}\)

\(\displaystyle-{22.81}\ +\ {22.81}={0}\) Substitute \(\displaystyle-{22.81}\ +\ {22.81}={0}\ \text{and}\ {70}\ +\ {22.81}={92.81}\ \text{in}\ {70}\ +\ {22.81}={y}\ -\ {22.81}\ +\ {22.81}\)

\(\displaystyle{92.81}={y}\ +\ {0}\)

\(\displaystyle{y}={92.81}\) Final siolution: \(\displaystyle{y}={92.81}\)