Number of terms is :

  ( 1000 - 1 ) : 2 + 1 = 500,5 

The sum is :

  ( 1000 + 1 ) x 500,5 : 2 = 250500,25

That worker makes 3 tools out of time is :

   12 hours - 7 hours 30 minute = 4 hours 30 minute

                                    =  4 ,5 hours

That worker makes a product time out is :

   4,5 : 3 = 1,5 ( hours )

\(\dfrac{5}{8}+\dfrac{9}{8}=\dfrac{5+9}{8}=\dfrac{14}{8}=\dfrac{7}{4}\)

\(\dfrac{6}{7}-\dfrac{3}{7}=\dfrac{6-3}{7}=\dfrac{3}{7}\)

( x + 1 ) . ( 1 + 1999 ) = 4000

x + 1 . 2000 = 4000

 x + 1 = 4000 : 2000

 x + 1 = 2 

  x =  2  - 1 

  x = 1

Number of female students is :

  40 x \(\dfrac{2}{5}\)= 16 ( student )

Number of male students is :

   40 - 16 = 24 ( student )

      Answer : 24 student