The height of dachshunds is usually 1/3 their length. If Mollie is 20 inches long, how tall is she?

This is a proportion problem.

Let's make her Length x and her height 1/3 x.

1/3 x = 20 inches

x = 6 2/3 inches

Molly's height is 6 2/3 inches.

Check it.

6 2/3 x 3 = ? (change the mixed number to a fraction)

20/3 x 3 = ? (multiply)

60/3 = ? (divide)

20 inches. Yes, it checks.

Mollie's height is approximately 6.6667 inches.