Riordan and Carl have some brown pens and some yellow pens. The number of yellow pens Riordan has is equal to the number of brown pens Carl has. ¹₃ of Riordan's pens are brown and ²₃ of Carl's pens are yellow. There are a total of 12 brown pens. Find the total number of pens they have.

Riordan		Carl		Total
Brown	Yellow	Brown	Yellow
	1x2	1x2
1x1	2x1	1x2	2x2
1 u	2 u	2 u	4 u	9 u

The number of Riordan's yellow pens and Carl's brown pens is the same.

The number of Riordan's yellow pens is repeated. The number of Carl's brown pens is repeated.  Make the number of Riordan's yellow pens and Carl's brown pens the same.  LCM of 2 and 3 is 2.

Number of brown pens
= 1 u + 2 u
= 3 u

3 u = 12

1 u = 12 ÷ 3 = 4

Total number of pens
= 1 u + 2 u + 2 u + 4 u
= 9 u
= 9 x 4
= 36

Answer(s): 36