Luis and Zeph have some yellow notebooks and some brown notebooks. The number of brown notebooks Luis has is equal to the number of yellow notebooks Zeph has. ²₃ of Luis's notebooks are yellow and ¹₃ of Zeph's notebooks are brown. There are a total of 72 yellow notebooks. Find the total number of notebooks they have.

Luis		Zeph		Total
Yellow	Brown	Yellow	Brown
	1x2	1x2
2x2	1x2	2x1	1x1
4 u	2 u	2 u	1 u	9 u

The number of Luis's brown notebooks and Zeph's yellow notebooks is the same.

The number of Luis's brown notebooks is repeated. The number of Zeph's yellow notebooks is repeated.  Make the number of Luis's brown notebooks and Zeph's yellow notebooks the same.  LCM of 1 and 3 is 2.

Number of yellow notebooks
= 4 u + 2 u
= 6 u

6 u = 72

1 u = 72 ÷ 6 = 12

Total number of notebooks
= 4 u + 2 u + 2 u + 1 u
= 9 u
= 9 x 12
= 108

Answer(s): 108