Eleven out of fifteen plus () one in fifteen equals the smallest prime number

Eleven out of fifteen plus () one in fifteen equals the smallest prime number

The smallest prime number is 2
（2-11/15）/(1/15)=30-11=19
Add 19 1 / 15

What's 11 out of 25?

11/25=0.44
Hope to solve the problem in time
If you are satisfied, please [adopt as a satisfactory answer]

99×（1－1/2）×（1－1/3）×（1－1/4）×…… Simple calculation of × (1-1 / 99)

99×（1－1/2）×（1－1/3）×（1－1/4）×…… ×（1－1/99）
=99×1/2×2/3×3/4…… ×98/99
=99×（1/2×2/3×3/4…… ×98/99）
=99×1/99
=1

Calculation: 1-2 + 3-4 + 5-6 +99-100 & nbsp; & nbsp; (required to write the necessary process)

1-2+3-4+5-6… +99-100  =（1-2）+（3-4）+（5-6）+… +（99-100）=-1-1-1-1-… -1=-50．