A fruit seller sells only starfruits and peaches. The ratio of starfruits to peaches is 1 : 3. A total of 108 fruits are added. The number of starfruits becomes 4 times as many as before and the number of peaches becomes 4 times as many as before. How many fruits are there in the end?

	Comparing starfruits at first and in the end	Starfruits	Peaches	Comparing peaches at first and in the end
Before	1x1 = 1 u	1 u	3 u	1x3 = 3 u
Change		+ 108
After	4x1 = 4 u	4 u	12 u	4x3 = 12 u

The number of peaches at first is repeated.  Make the number of peaches at first the same.  LCM of 1 and 3 is 3.

The number of starfruits at first is repeated. Make the number of starfruits at first the same. LCM of 1 and 1 is 1.

Number of fruits at first
= 1 u + 3 u
= 4 u

Number of fruits in the end
= 4 u + 12 u
= 16 u

Number of fruits added
= 16 u - 4 u 
= 12 u

12 u = 108

1 u = 108 ÷ 12 = 9

Number of fruits in the end
= 16 u
= 16 x 9
= 144

Answer(s): 144