Factorial
There is a notation which will be used many times in the next explanation. That notation is called factorial. Factorial is notated by: “!”. Factorial is the short writing of a series of multiplication of positive number in a decreasing order until 1.
Factorial can be defined as the following:

And so on.
Generally the factorial of a numeral is formulated as the following:

n!=n∙(n-1)∙(n-2)∙…∙1=n∙(n-1)!
Example 5:

Exercise Competency Test 5 (QnA factorial concept)
1. 6!=⋯
A. 720 B. 620 C. 520 D. 360 E. 6
Answer: A, explanation:

6×5×4×3×2×1=7202. 5!∙3!=⋯
A. 15! B. 10! C. 8! D. 7! E. 6!
Answer: E, explanation:

5!×3×2×1=6×5!=6!3. 8!/5!=⋯
A. 336 B. 326 C. 316 D. 236 E. 226
Answer: A, explanation:

4. 7!/(4!∙3!)=⋯
A. 70 B. 50 C. 35 D. 25 E. 10
Answer: C, explanation:

5. n!/(n-1)!=⋯
A. n C.n-2 E. 1/n
B. n-1 D. n²–n
Answer: A, explanation:

6. Suppose p and q are the roots of quadratic equation x²-14x+48=0. If p>q, then the value of

Answer: C, explanation:

7. If

The n=⋯
A. 6 B. 5 C. 4 D. 3 E. 2
Answer: B, explanation:

8. If

Then the value of n which satisfy the equation is equal to ….
A. 4 B. 5 C. 6 D. 7 E. 8
Answer: B, explanation: