SP LK runs: is my math correct?

1.13c. SP, /players 7, LK runs. Kinda new to LK. Have been running for 5-6 hours I think? 2 Sur. So not bad.

Every time I run, I buy 8 sets of keys. I run until the keys run out. I only pick up Pul+. At the end of the run, I count how many runes I got.

For the most recent few runs, I got nothing at all. So I checked how many I'm supposed to get on average. Below is my math.

How many chests I opened: 8 sets of keys * 12 keys per set * 5 chests average to 1 locked chest = 480.

For each superchest, it has 65534 patterns. From the chest calc, I see there are 80 patterns which contain Pul+.

So, on average, one run should hit this many patterns which contains Pul+: 480 * 80 / 65534 = 0.586

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Is the above is correct, then I'm just getting unlucky in the last few runs, I guess.

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--EDIT--

And from the 80 patterns, I get the following runes (total up to 80).

> Ber Sur Lo Ohm Vex Gul Ist Mal Um Pul

> 2 9 2 5 6 11 5 14 10 16

So, on average, one pattern is worth this many Surs: (2 * 2 + 9 * 1 + 2 * 1/2 + 5 * 1/4 + ...) / 80 = 0.215.

So each run provides 0.586 * 0.215 = 0.126 Surs.

So to get one Sur, I need to do 1 / 0.126 = 7.9 runs.

Suppose each map has 6 chests and takes 30 sec (including save/load), or 12 chests per minute, to hit 480 chests (one run) I need 480 / 12 = 40 minutes.

That means to get one Sur, it will take me 7.9 * 40 minutes = 5.27 hours.

Does this sound correct?

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