Answer:
1st son (oldest): 21
2nd: 11
3rd: 5
4th (youngest): 2
Explanation:
1st son gets half: 39/2 = 19.5 round up to 20
2nd son gets 1/4: 39/4 = 9.75 round up to 10
3rd son gets 1/8: 30/8 = 3.75 round up to 4
Number of camels left now: 39 - 20 - 10 - 4 = 5
The youngest son is only supposed to get 1/10 (39/10 = 0.39) which rounds up to 1 camel, but there are 5 camels available. So the fair thing to do (?) is give the youngest 2 camels and give each of the older sons one extra camel.
Final tally:
1st: 21
2nd: 11
3rd: 5
4th: 2