Basic Mathematics for College Students

2.3 Subtracting Integers 161

Self Check 7

CRUDE OILOn Wednesday, the

level of crude oil in a storage

tank was 5 feet above standard

capacity. Thursday, after a large

refining session, the level fell to

a mark 76 feet below standard

capacity. Find the change in the

crude oil level from Wednesday to

Thursday.

Now TryProblem 103

− 14 0 16

Friday Monday

Using Your CALCULATOR Subtraction with Negative Numbers

The world’s highest peak is Mount

Everest in the Himalayas. The

greatest ocean depth yet measured

lies in the Mariana Trench near the

island of Guam in the western

Pacific. To find the range between

the highest peak and the greatest

depth, we must subtract:

To perform this subtraction on a calculator, we enter the following:

Reverse entry: 29035 36025

Direct entry: 29035 36025

The range is 65,060 feet between the highest peak and the lowest depth.

(We could also write as and then use the

addition key to find the answer.)

29,035(36,025) 29,03536,025

 () ENTER 65060

 / 

29,035(36,025)

AnalyzeIt is helpful to list the given facts and what you are to find.

• On Monday, the water level was 16 feet above normal. Given


• On Friday, the water level was 14 feet below normal. Given


• Find the change in the water level. Find

Form To find the change in the water level, we subtract the earlier value from the
later value.The water levels of 16 feet above normal (the earlier value) and 14 feet
below normal (the later value) can be represented by 16 and.
We translate the words of the problem to numbers and symbols.

is equal to minus

16

SolveWe can use the rule for subtraction to find the difference.

Add the opposite of 16, which is 16.

Use the rule for adding integers with the same sign.

StateThe negative result means the water level fell30 feet from Monday to
Friday.

CheckIf we represent the change in water level on a horizontal number line, we
see that the water level fell 16  14  30 units. The result checks.

 30

 14  16  14 (16)

  14 

The change in

the water level

the earlier water

level (Monday).

the later water

level (Friday)

The change in

the water level

 14

Sea level

Mariana

Trench

Mt. Everest 29,035 ft

–36,025 ft

1. a. b. 12 c. 2. a. 3 b. 3. 4. 5. 6 6.125ºF
   7.The crude oil level fell 81 ft.

 5  79  3  7  15

ANSWERS TO SELF CHECKS