I got 6 attack 7 str, 3% str first try, and I'm happy about it after I did the math:
Chance of chaos scroll increasing attack by 3-5: 60% * (3/11) = 16%
Chance of 3 scrolls raising your attack: 0.16^3 = 0.44%
Average amount of tries to archieve this: 0.0044^-1 = 228
Chaos scrolls needed on average (considering you stop scrolling after each fail): 228*(1-16%) + 2* 228*(16%)*(1-16%) + 3* 228*(16%)^2*(1-16%) + 3 = 271
Mesos needed, considering 25m/CS and 7.5m/cleanshoulder: 228*7.5 + 271 * 25 = 8.51b
And that's not even considering your primary stat being nice, or a 90% potential blowing it up.
PS: 5 att minimum (= scrollsucceschance 60% * (3/11) = 27%) needs 66 chaos scrolls.
Chance of chaos scroll increasing attack by 3-5: 60% * (3/11) = 16%
Chance of 3 scrolls raising your attack: 0.16^3 = 0.44%
Average amount of tries to archieve this: 0.0044^-1 = 228
Chaos scrolls needed on average (considering you stop scrolling after each fail): 228*(1-16%) + 2* 228*(16%)*(1-16%) + 3* 228*(16%)^2*(1-16%) + 3 = 271
Mesos needed, considering 25m/CS and 7.5m/cleanshoulder: 228*7.5 + 271 * 25 = 8.51b
And that's not even considering your primary stat being nice, or a 90% potential blowing it up.
PS: 5 att minimum (= scrollsucceschance 60% * (3/11) = 27%) needs 66 chaos scrolls.