10% of Bobby's savings was $30 more than 30% of Andy's savings. After Bobby spent ¹₂ of his savings and Andy spent 40% of his savings, Andy had $231 less than Bobby. How much was Andy's saving at first?

	Andy	Bobby
Before	10 u	30 u + 300
Change	- 4 u	- 15 u - 150
After	6 u	15 u + 150
Comparing Andy and Bobby in the end		231 more

10% = ¹⁰₁₀₀ = ¹₁₀

30% = ³⁰₁₀₀ = ³₁₀

¹₁₀ Bobby = ³₁₀ Andy + 30 

Make the numerators the same. LCM of 1 and 3 is 3.
 
1x310x3 Bobby = 3x110x1 Andy + 30 
330 Bobby = 310 Andy + 30 

Simplify the fractions.
¹₃₀ Bobby = ¹₁₀ Andy + 10

Let ¹₁₀ Andy be 1 u.

Andy's savings at first = 10 u

¹₃₀ Bobby = ¹₁₀ Andy + 10
Let ¹₃₀ Bobby be 1 u + 10.

Bobby's savings at first
= 30 x (1 u + 10) 
= 30 u + 300

Savings that Andy spent
= 40% x 10 u
= ⁴⁰₁₀₀ x 10 u
= 4 u

Savings that Bobby spent 
= ¹₂ x (30 u + 300)
= 15 u + 150 

Andy had $231 less than Bobby in the end. If another $231 was given to Andy, the amount that each had in the end would be the same.

15 u + 150 = 6 u + 231 
15 u - 6 u = 231 - 150
9 u = 81

1 u = 81 ÷ 9 = 9

Savings that Andy had at first
= 10 u 
= 10 x 9
= $90

Answer(s): $90