Explanation:
We are adding two numbers:
1.86
+ 38.577
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First, line up the decimal points:
1.860
+ 38.577
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Now add column by column from right to left:
- Thousandths place: 0 + 7 = 7
- Hundredths place: 6 + 7 = 13 → write 3, carry 1
- Tenths place: 8 + 5 + 1 (carry) = 14 → write 4, carry 1
- Units place: 1 + 8 + 1 (carry) = 10 → write 0, carry 1
- Tens place: 0 + 3 + 1 (carry) = 4
So the sum is
40.437, as shown.
Now, the question is about
significant figures for addition/subtraction.
Rule: For addition and subtraction, the answer should be rounded to the
least precise decimal place — that is, the farthest right decimal place that any number in the problem has.
Let’s look at each number:
- 1.86 → has digits to the
hundredths place (2 decimal places)
- 38.577 → has digits to the
thousandths place (3 decimal places)
The *least precise* is 1.86 — it only goes to hundredths. So our final answer must be rounded to the
hundredths place.
Our unrounded sum is:
40.437
Rounding to the hundredths place means we look at the
thousandths digit, which is
7.
Since 7 ≥ 5, we round
up the hundredths digit (3 → 4).
So:
40.437 → rounded to hundredths =
40.44
Final Answer:
40.44
Parent Tip: Review the logic above to help your child master the concept of adding and subtracting sig figs with.
