how to teach subtraction of decimal numbers

Answer: To subtract decimal numbers: (1) Annex trailing zeros to convert into like decimals, (2) Line up the decimal points vertically, (3) Subtract digits column by column from right to left with borrowing where needed, and (4) Drop the decimal point straight down into the difference.

Step-by-step solution

Step 1: Convert unlike decimals to like decimals

To subtract decimal numbers, first observe the number of digits after the decimal point. The number $5.3$ has $1$ decimal place (tenths), while $2.58$ has $2$ decimal places (hundredths). Write extra zeros at the end of $5.3$ to make it $5.30$ so that both numbers have the same number of decimal digits.

Step 2: Align numbers vertically by the decimal point

Write the numbers one below the other such that the decimal points lie in the exact same vertical column. This ensures that tens align with tens, ones with ones, tenths with tenths, and hundredths with hundredths.

Step 3: Regroup and subtract from right to left

Subtract just like whole numbers, starting from the rightmost column. In the hundredths column, since we cannot take $8$ from $0$ , borrow $1$ tenth from $3$ tenths to make $10$ hundredths; $10 - 8 = 2$ . In the tenths column, borrow $1$ one from $5$ ones to make $12$ tenths; $12 - 5 = 7$ . In the ones column, $4 - 2 = 2$ . Place the decimal point directly below the other decimal points to get $2.72$ .

Step 4: Verify by addition

To check the result, add the difference $2.72$ back to the subtrahend $2.58$ . The sum equals $5.30$ , which confirms that the subtraction is correct.

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