Acookie factory uses 1/10 of a bag of flour in each batch of cookies. the factory used 1/2 of a bag of flour yesterday. how many batches of cookies did the factory make?

The factory made 5 batches. 1/10 of flour for each batch. 1/2 = 5/10 So they made 5 batches of cookies.

1/10 per batch
1/2 used
they made 5 batches cause, that is what is 10 is halved by. For ex: I used 1/2 bags of flour and each batch uses 1/20 bags of flower. How many batches did I make. This is 10.
All you need to do is take the denominator, and cut it in half, cause that is how much was used. and 10 divided by 2 is 5. 

5b - 5 + 10, when b = 5.

(5×5) - 5 + 10

= 25 - 5 + 10

= 20 + 10

= 30