In a shop, some mini-helicopters and rubber balls were on sale. ¹₂ of the items were mini-helicopters. ¹₃ of the mini-helicopters and 130 rubber balls were sold. There were ¹₉ of the items left in the shop. How many mini-helicopters and rubber balls were there in the shop at first?

	Mini-helicopters	Rubber balls	Total
Comparing mini-helicopters  and rubber balls at first	1x9 = 9 u	1x9 = 9 u	2x9 = 18 u
Before	3x3 =  9 u		9x2 = 18 u
Change	- 1x3 = - 3 u	- 130	- 8x2 = - 16 u
After	2x3 = 6 u	-4 u	1x2 = 2 u

 
The total number of toys at first is repeated.  Make the total number of toys at first the same. LCM of 2 and 9 is 18.

The number of mini-helicopters at first is repeated.  Make the number of mini-helicopters the same. LCM of 9 and 3 is 9. 

Number of rubber balls left
= 2 u - 6 u
= -4 u

Number of rubber balls sold
= 9 u - -4 u
= 13 u

13 u = 130

1 u = 130 ÷ 13 = 10

Number of mini-helicopters and rubber balls at first
= 18 u
= 18 x 10
= 180

Answer(s): 180