Final answer:
The other number is -400 when the sum of two numbers is -890 and one of the numbers is -490 because -890 + 490 = -400.
Step-by-step explanation:
To find the other number when the sum of two numbers is -890 and one of the numbers is -490, we can set up the equation -490 + x = -890, where x represents the other number. Following the rules for adding and subtracting numbers with different signs, we change the sign of -490 to +490 and then subtract it from -890:
-890 + 490 = x
Adding the two numbers, we get:
-400 = x
Therefore, the other number is -400.