Xuan has 30% as many erasers as Risa. Risa has 140% as many erasers as Tammy. If Risa gives 30 erasers to Tammy, both will then have an equal number of erasers. Find the average number of erasers the three of them have.

Xuan	Risa	Tammy
3x7	10x7
	7x10	5x10
21 u	70 u	50 u

30% = ³⁰₁₀₀ = ³₁₀
140% = ¹⁴⁰₁₀₀= ⁷₅

The number of erasers that Xuan has is repeated.  Make the number of erasers that Xuan has the same. LCM of 10 and 7 is 70.

	Risa	Tammy	Total
Before	70 u	50 u	120 u
Change	- 10 u	+ 10 u
After	60 u	60 u	120 u

Total number of erasers that Risa and Tammy have
= 70 u + 50 u
= 120 u

After Risa gives to Tammy, both of them will have the same number of erasers. 

The total number of erasers that Risa and Tammy have remains unchanged.

Number of erasers that each of them will have
= 120 u ÷ 2
= 60 u

Number of erasers that Risa gives to Tammy
= 70 u - 60 u
= 10 u

10 u = 30

1 u = 30 ÷ 10 = 3

Total number of erasers that three of them have
= 120 u + 21 u
= 141 u

Average number of erasers that each of them have
= 141 u ÷ 3
= 47 u
= 47 x 3
= 141

Answer(s): 141