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2-10.

Add or subtract.  Remember to line up the decimal points.   

Compute without a calculator

  1.  

    Line the problem up vertically. Numbers arranged in 2 rows of 7 columns as follows: Top row: 5, 3, decimal, 1, 9, 9. Bottom row: 2, 7, decimal, 6, 1, blank.

    Add a zero and subtract. Digit 0 added under last 9. Answer has 9 in far right column.

    Continue subtracting going from right to left. Answer has 8, left of 9.

    Borrow 1 from the 3. Then subtract 6 from 11. Changes: top row, 3 to 2, 1 to 11, answer add 5 left of 8.

    Borrow again. Changes: top row, 5 to 4, 2 to 12.

  2.  

    The 2 numbers are stacked in vertical columns as follows: 1 and blank, 5 and 5, 5 and 6, decimal and decimal, 9 and 2, 6 and 3, blank and 2.

    Add from right to left, carrying when necessary. Now finish the problem. Changes: top row: 1 above 5 in 3rd column and 0 in last column, answer: first 3 columns are blank, then decimal, 1, 9, and 2.

  3.  

    See part (a).