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

Opal	Mary	Diana
3x7	10x7
	7x10	5x10
21 u	70 u	50 u

30% = ³⁰₁₀₀ = ³₁₀
140% = ¹⁴⁰₁₀₀= ⁷₅

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

	Mary	Diana	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 Mary and Diana have
= 70 u + 50 u
= 120 u

After Mary gives to Diana, both of them will have the same number of erasers. 

The total number of erasers that Mary and Diana have remains unchanged.

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

Number of erasers that Mary gives to Diana
= 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