This problem can be solved using proprtions. Once you set up the proportion, the calculations are easy.
Let x = number of pens made in 1 second.
[tex]\frac{9pen}{3sec} = \frac{xpen}{1 second}[/tex]
Now, you just cross multiply and solve.
9 = 3x
x = 3
The rate is 3 pens per second.
