At the beginning of the week, the ratio of cats to dogs at Glenna's Pet Store was 4 to 5. By the end of
the week, the number of cats had doubled, while the
number of dogs had increased by 12. If the ratio of
cats to dogs at the end of the week was 1 to 1, how
many cats did the store have at the beginning of the
week?

Answer is in the file below

cutt.ly/tz3yDpb

9

Step-by-step explanation:

Call the Total Amount of money he had X.

Amount he used to buy pens: 3/8X

Amount of money left after buying pens: X - 3/8X = 5/8X

Amount he used to buy notebooks: 2/5 * 5/8X = 1/4X

1/4X or 2/8X for 2 notebooks, so if he spent 3/8X for notebooks, he would get 3 notebooks.

As a notebook cost 3 times a pens, so for 3/8X money, he bought 9 pens.