Oliver has 70% as many erasers as Flynn. If Oliver gives away 25% of the erasers and Flynn gives away 20% of his erasers, they will have 318 erasers altogether. How many erasers do the two of them have?

	Oliver	Flynn	Total
Comparing Oliver and Flynn at first	7x4 = 28 u	10x4 = 40 u
Before	4x7 = 28 u	5x8 =  40 u
Change	- 1x7 = - 7 u	- 1x8 = - 8 u
After	3x7 = 21 u	4x8 = 32 u	318

70% = ⁷⁰₁₀₀ = ⁷₁₀

25% = ²⁵₁₀₀ = ¹₄ 

20% =²⁰₁₀₀ = ¹₅ 

The number of erasers that Oliver has at first is repeated.  Make the number of erasers that Oliver has the same.  LCM of 7 and 4 is 28 u.

The number of erasers that Flynn has at first is repeated. Make the number of erasers that Flynn has the same. LCM of 10 and 5 is 40 u.

Number of erasers in the end
= 21 u + 32 u
= 53 u

53 u = 318

1 u = 318 ÷ 53 = 6

Total number of erasers that the two of them have
= 28 u + 40 u
= 68 u
= 68 x 6
= 408

Answer(s): 408