You buy a 625.05 mL container of dish soap. You already have 142.71 at home. How many mL do you have in total
The Correct Answer and Explanation is:
Answer: 767.76 mL
When you add liquid volumes, the first rule is to keep the unit identical—in this case millilitres (mL). Because both measurements already use mL, you can combine them directly without converting.
Start by writing the two quantities underneath one another with their decimal points aligned:
625.05
+ 142.71
Lining up the decimal points ensures that each column represents the same place value: hundredths, tenths, ones, tens, and hundreds. Working from right to left:
• Hundredths: 5 + 1 = 6
• Tenths: 0 + 7 = 7
• Ones: 5 + 2 = 7
• Tens: 2 + 4 = 6
• Hundreds: 6 + 1 = 7
The completed sum is 767.76, and the decimal point is placed directly beneath the other decimal points to retain proper structure.
Why does the answer make sense? A rough estimate can reassure you. Round 625.05 mL down to 625 mL and 142.71 mL up to 143 mL. Adding 625 + 143 gives 768 mL, virtually identical to 767.76 mL. Because the rounded figures were chosen to balance each other—one lower, one higher—the close agreement confirms that no major error crept in.
Context also helps. One litre equals 1 000 mL, so 767.76 mL is a bit over three-quarters of a litre. If a typical sinkful of dishes takes about 10 mL of soap, this supply would last around 76 washings, or roughly two and a half months if you wash dishes once a day. Thinking in these everyday terms turns an abstract sum into a concrete appreciation of how long your soap will actually last.
Taking time to align decimals, verify the unit, estimate mentally, and interpret practically not only produces the correct total but strengthens number sense for future household calculations. This method works for any decimals you encounter.
