Final answer:
Aligning numbers by place value when adding decimals ensures the accuracy and correctness of your computation. The sum should contain the same number of digits to the right of the decimal as the least certain number used, thereby accurately representing the certainty of your values.
Step-by-step explanation:
The importance of lining up numbers according to place value when adding decimals lies in maintaining accuracy and precision of your results. When adding decimals, the sum should contain as many digits to the right of the decimal as in the least certain of the numbers you used. If you are adding two numbers and one has a decimal point at the thousandths place, and the other at the tenths place, even if you were to be correct in your addition, you would be representing your answer incorrectly if you didn't line the numbers up by place value.
Let's take an example: 0.3 (decimal till tenths place) + 0.04 (decimal till hundredths place). You line the numbers up like this:
0.30
0.04+
Which sums to 0.34. If you did not line up the numbers by place value, you might mistakenly add them as 0.3 + 0.4, which would give you a wrong result. Therefore, lining up place values helps in maintaining the correctness of the calculation and properly representing the certainty of your values.
Learn more about Adding Decimals