Problem 1 :
Evaluate :
(-4) + (-7)
Problem 2 :
Evaluate :
(+5) + (+8)
Problem 3 :
Evaluate :
(-1) + (-2)
Problem 4 :
Use model to find the sum of -5 and -2.
Problem 5 :
The temperature was 2°F below zero. The temperature drops by 5°F. What is the temperature now ?
Problem 1 :
Evaluate :
(-4) + (-7)
Solution :
Step 1 :
Find the absolute values.
|-4| = 4 and |-7| = 7
Step 2 :
Find the sum of the absolute values :
4 + 7 = 11
Step 3 :
Use the sign of the integers to write the sum.
(-4) + (-7) = -11
Problem 2 :
Evaluate :
(+5) + (+8)
Solution :
Step 1 :
Find the absolute values.
|+5| = 5 and |+8| = 8
Step 2 :
Find the sum of the absolute values :
5 + 8 = 13
Step 3 :
Use the sign of the integers to write the sum.
(+5) + (+8) = +13
Problem 3 :
Evaluate :
(-1) + (-2)
Solution :
Step 1 :
Find the absolute values.
|-1| = 1 and |-2| = 2
Step 2 :
Find the sum of the absolute values :
1 + 2 = 3
Step 3 :
Use the sign of the integers to write the sum.
(-1) + (-2) = -3
Problem 4 :
Use model to find the sum of -5 and -2.
Solution :
Let us take five negative counters for -5 and two negative counters in the second row for -2.
In the above figure, we find seven negative counters in total.
So, the answer is -7.
Therefore,
(-5) + (-2) = -7
Problem 5 :
The temperature was 2°F below zero. The temperature drops by 5°F. What is the temperature now ?
Solution :
Step 1 :
According to the question, the initial temperature was 2°F below zero. 2 below zero is -2.
So, the initial temperature is -2°F
Step 2 :
Let us mark the initial temperature on the number line.
Step 3 :
A drop in temperature of 5° is like adding -5° to the temperature.
Since the temperature is dropping, we have to go below the initial temperature. The temperature drops by 5°. So, we have to count 5 units on the number line below -2 to find the final temperature.
That is -7.
Mark the temperature now on the number line.
Step 4 :
From the above figure, the final temperature is -7°.
Justify and Evaluate :
In the above example, we have just added -2 and -5.
From the above example problem, it is clear that when we add two negative numbers, we have to add them as usual and take negative sign to the result.
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