Use a calculator to find the sum. Estimate the sum by rounding to check that your answer is reasonable.

– 345 + (– 978)

Rule: The sum of any integer and its opposite is equal to zero.

Explanation: Adding two positive integers always yields a positive sum; adding two negative integers always yields a negative sum. To find the sum of a positive and a negative integer, take the absolute value of each integer and then subtract these values.

To add two numbers with the same sign, first add the two numbers ignoring the sign and then put their common sign before the answer.

To add two numbers with the opposite sign, ignore their signs and subtract the smaller number from the bigger number. Then put the sign of the bigger number before the answer.

To add two integers, we need to check the signs of those two integers.

Rule: If they are with the same sign (positive or negative),first add the two numbers ignoring the sign and then put their common sign (positive or negative) before the answer.

Here both the numbers are negative, we need to add the numbers and put their common sign negative before the answer.

Now Evaluate:– 345 + (– 978)

$-345+(-978)=-345-978=-1323$

We can write: – 345 + (– 978) = – 1323