Each packet of large cookies weighs $\frac{2}{5}$oz and each small packet of cookies weighs $\frac{3}{8}$oz. What is the total weight of 1 large packet of cookies and 1 small packet of cookies?

The correct option is A $\frac{31}{40}$ oz
Weight of large packet of cookies = $\frac{2}{5}$oz
Weight of small packet of cookies = $\frac{3}{8}$oz
Total weight of the cookies = $\frac{2}{5}+\frac{3}{8}$

As these are unlike fractions, let's convert them into the like fractions by finding LCM of denominators 5 and 8.

Multiple of 5: 5, 10, 15, 20, 25, 30, 35, 40 ..
Multiple of 8: 8, 16, 24, 32, 40 ...
$\therefore$ LCM (5, 8) = 40

Now covert the denominators of each fractions into 40 (LCM of 5 and 8)
Multiplying the fraction $\frac{2}{5}$ with 8, we get:
$\frac{2}{5}=\frac{8\times 2}{8\times 5}=\frac{16}{40}$

Multiplying the fraction $\frac{3}{8}$ with 5, we get:
$\frac{3}{8}=\frac{5\times 3}{5\times 8}=\frac{15}{40}$

Now, add the two fractions
Total weight of the cookies $=\frac{2}{5}+\frac{3}{8}=\frac{16}{40}+\frac{15}{40}=\frac{16+15}{40}=\frac{31}{40}$

Hence, total weight of the cookies is $\frac{31}{40}$oz.