Question

What is the value of

Answer 1

Answer:

D. 76.5

Step-by-step explanation:

The summation sign means that it is the sum of the expression for all values of n upto 6.

n = 2 below the summation sign means that n starts from 2.

∑(n-1)!/2 from n= 2 to n=6

= (2-1)!/2 + (3-1)!/2 + (4-1)!/2 + (5-1)!/2 + (6-1)!/2

= 1!/2 + 2!/2 + 3!/2 + 4!/2 + 5!/2

= 1/2 + 2*1/2 + 3*2/2 + 4*3*2/2 + 5*4*3*2/2

= 1/2 + 2/2 + 6/2 + 24/2 + 120/2

= 0.5 + 1 + 3 + 12 + 60

= 76.5

Answer 2

$\displaystyle\\\sum_{n=2}^6\dfrac{(n-1)!}{2}=\dfrac{(2-1)!}{2}+\dfrac{(3-1)!}{2}+\dfrac{(4-1)!}{2}+\dfrac{(5-1)!}{2}+\dfrac{(6-1)!}{2}=\\\\=\dfrac{1}{2}+\dfrac{2}{2}+\dfrac{6}{2}+\dfrac{24}{2}+\dfrac{120}{2}=0.5+1+3+12+60=76.5$