Final answer:
To add 4.2 and -0.4 together, combine the two numbers. 4.2 + (-0.4) is equal to 3.8.
Step-by-step explanation:
To add 4.2 and -0.4 together, you simply combine the two numbers. Remember that adding a negative number is the same as subtracting a positive number. In this case, 4.2 + (-0.4) equals 3.8.
If we plot the first addend, 4.2, on a number line, it would fall on the positive side, towards 4. Starting from there, if we go 0.4 units in the negative direction, we would end up at 3.8, which is the sum.
Learn more about Adding and subtracting decimals