Question

Bob added the numbers 5.6 and 1.9 and got 6.15. How might Bob have gotten this answer? Explain to Bob why his answer is not correct and why the correct method for adding decimal numbers makes sense.

Answer 1

Bob made a mistake by not accounting for the decimal point placement when adding the numbers 5.6 and 1.9 which led him to wrongly calculate the sum as 6.15. The correct way of adding decimals is to align decimal points and observe the place values when adding, which gives the correct sum 7.5.

Step-by-step explanation:

It appears Bob has made a common error when adding decimal numbers. It seems like he added the numbers as if they were whole numbers, not taking into account the placement of the decimal point. The numbers 5.6 and 1.9 should be added straightforwardly by aligning and adding the decimal and the numbers separately, not by adding them as they were whole numbers.

This means Bob should proceed by adding like this: there is 5 on the left side of the decimal point in the number 5.6, and 1 on the left side of the decimal in 1.9. Those two should add up to 6. On the right side of the decimal point, Bob has 6 in 5.6 and 9 in 1.9, which add up to 15. Since 15 is a two-digit number and we only have space for one digit after decimal, we write down 5 and carry 1 to the next place value (to the left of the decimal point). So the correct answer to 5.6 + 1.9 is 7.5.

Steps:

1. Align the numbers by their decimal points.
2. Add the numbers to the right of the decimal point (6 + 9 = 15).
3. Write down the 5 and carry 1 over to the place on the left of the decimal point.
4. Add the numbers to the left of the decimal point, including the carried number (5 + 1 + 1 = 7).
5. Insert the decimal point in between the numbers in the answer. So the answer is 7.5

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Answer 2

Bob made a mistake in adding decimals because he failed to align the decimal points and add each column from right to left. The correct total of 5.6 and 1.9 is 7.5, not 6.15. His confusion likely arose from place value, which behaves differently in decimal numbers.

Step-by-step explanation:

The subject is Mathematics, specifically addition of decimal numbers. It seems that Bob may have misunderstood the correct process for adding decimals. When Bob added 5.6 and 1.9, he got 6.15 as a result. This is not correct because when we add decimal numbers, we have to align the decimal points and add each column from right to left.

The correct addition of 5.6 and 1.9 should be as follows: align the decimal points and add from right to left, just as you would with whole numbers. So, 5.6 and 1.9 equals 7.5, not 6.15.

I think where Bob got confused was he might have added the 5 and 1 together to get 6, and then added the .6 and .9 together to get 1.5 (Note: .6 + .9 is actually 1.5, but decimal addition requires us to carry the '1' to the integer's place, and not place after decimal). Hence, his result of 6.15. So, while his concept of addition was correct, the method of application was incorrect when it comes to decimals.

Learn more about Adding Decimal Numbers