Question

David inherited some money from his uncle. He invested half of the money with Bernie

Answer 1

Given:
Let x be the whole amount inherited.
1/2 * x - invested with Bernie Madoff
1/3 * x - lost due to identity theft
1/8 * x - lost in casino
40,000 - remainder

x - x/2 - x/3 - x/8 = 40,000

LCM: 
2: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24
3: 3, 6, 9, 12, 15, 18, 21, 24
8: 8, 16, 24, 

   x * 24/24 = 24x / 24
x/2 * 12/12 = 12x / 24
x/3 *   8/8   = 8x / 24
x/8 *   3/3   = 3x / 24
40,000 * 24/24 = 960,000 / 24

24x/24 - 12x/24 - 8x/24 - 3x/24 = 960,000/24
(24x - 12x - 8x - 3x)/24 = 960,000/24
x/24 = 960,000/24
24 * x/24 = 24 * 960,000/24
x = 960,000

x = 960,000 initial inheritance
x/2 = 960,000/2 = 480,000 invested with Bernie Madoff
x/3 = 960,000/3 = 320,000 lost due to identity theft
x/8 = 960,000/8 = 120,000 lost in the casino
40,000 - remaining amount.

960k - 480k - 320k - 120k = 40k
40k = 40k