1. The problem is to calculate sums and differences of decimals. 2. The rule for adding or subtracting decimals is to align the decimal points vertically. 3. Add or subtract the digits column by column, starting from the right. 4. Keep the decimal point in the answer aligned with the numbers. 5. Calculate each: - $800.54 + 90.52 = 891.06$ - $343.4 + 5.607 = 349.007$ - $94.9 - 41.871 = 53.029$ - $809.144 - 15.96 = 793.184$ - $803.309 - 133.36 = 669.949$ - $767.3 - 24.9 = 742.4$ - $489.08 - 4.2 = 484.88$ - $921.74 + 2.7 = 924.44$ - $384.94 + 17.348 = 402.288$ - $260.65 - 40.9 = 219.75$ - $67.1 - 1.19 = 65.91$ - $35.438 - 17.2 = 18.238$ - $686.4 - 199.61 = 486.79$ - $6.356 + 5.8 = 12.156$ - $75.715 + 30.5 = 106.215$ - $89.88 - 48.8 = 41.08$ - $3.7 + 1.5 = 5.2$ - $64.32 + 21.63 = 85.95$ - $875.75 + 26.64 = 902.39$ - $656.86 + 46.37 = 703.23$ Each answer keeps the decimal point aligned and sums or subtracts the digits correctly. This method works for all decimal addition and subtraction problems.