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

     Answer : 1,5 hours

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

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

( 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 students