(Premium Prep) Cisco 500-444 Real Exam Questions

Study Notes

Subtraction is an arithmetic operation that represents the removal of objects from a collection.
It is the inverse of addition, as adding the result back to the difference will recover the original value.
Subtraction is denoted by the minus sign (-)
Example: 10 - 5 = 5

Commutative Property: Does not apply. For example 5 - 3 ≠ 3 - 5
Associative Property: Does not apply. For example (10 - 5) - 2 ≠ 10 - (5 - 2)
Identity Property: The only identity element in subtraction is subtracting 0 from a number, which results in that same number. For example, 10 - 0 = 10
Distributive Property: Can be used in some cases; for example, 100 - (30 + 20) = (100 - 30) - 20 or 100 - 50 = 70

Word problems involving subtraction frequently involve taking away, comparisons, or finding differences.
Key words often indicate subtraction: minus, less, difference between, fewer than, taken away, left
Example: Mary has 15 apples and gives 5 to her friend. How many apples does Mary have left? Problem type: Take Away problem, answer is 10 apples. Example: John has 10 stamps and Tom has 8 stamps. How many more stamps does John have? Problem type: Comparison problem. Answer is 2 extra stamps.

Compensation Subtraction: Adjust numbers to make subtraction easier by adding or subtracting values from both numbers by the same amount to get a "nice" number. Example: 87 - 28 ≈ (87+2) - (28+2) = 89 - 30 = 59
Using Compatible Numbers: Use pairs of numbers that are easy to subtract mentally. Example: 65 - 23 ≈ 65-20 -3 = 45-3 = 42
Break-down Method: Separating a subtraction problem into simpler ones. Example: 98-36 can be separated into 98-30-6=68-6=62

Subtraction and addition are inverse operations.
Knowing the basic addition facts greatly helps in accurate subtraction.
Memorisation of subtraction facts is important to speed up basic calculations. For example: being able to instantly know the difference between quantities can create huge time savings.