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2-28.

Add or subtract.   

Compute without a calculator

  1. Numbers arranged in 3 rows of 5 columns as follows: Top row: blank, blank, 9, decimal, 6, 7. Middle row: 4, 9, decimal, 7, 0. Bottom row: blank, 5, decimal, 2, 2. 

    Add the numbers in the hundredths place. Changes: Answer row has 9 in last column.

    Add the numbers in the tenths place. Since the sum is digits, place the first digit () in the column to the left. Changes: Top row: 1above the 9. Answer row: 5in fourth column.

    Add the numbers in the ones place. Since the sum is digits, place the first digit () in the column to the left. Changes: Middle row has 2 above the 4. Answer row has 4 in second column and decimal in third column.

    Add the numbers in the tens place. Changes: Answer row has 6 in first column.

  1. See part (a). Be careful to line up the decimals correctly.

  • Numbers arranged in 2rows of 5 columns as follows: top row: 9, 7, decimal, 1, blank. bottom row: 3, 5, decimal, 0, 4.

    Since is less than in the hundredths place, borrow from the column to the left, making the hundredths place Changes: top row, fourth column is 0, last column is 10. Added to answer row has, 6 in last column.

    Now the tenths place is Added to Answer row: 0 in fourth column.

    Subtract the numbers in the ones place. Added to Answer row: 2 in second column, decimal in third column.

    Subtract the numbers in the tens place. Added to answer row: 6 in first column.