The expression is
Place value chart for 5.8 and 4.2.
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Line up the decimal points and draw a line below the numbers.
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First find the sum of the tenths digit.
\The sum of the tenths digit .
The sum is 10, so carry digits to the next column on the left
\Next find the sum of the ones digit.
\The sum of the ones digit .
The sum is 10, so carry the tens digit to the next column on the left
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