I guessed between 500 and 700 because there are 4x10 blocks (40) with a range between 0 and 40 tickets per block (time slot). But in fact the top two rows are almost empty, and the bottom two have many tickets left.

That makes:

Max = 40 slots x 40 tickets div 2 rows = 1600 div 2 = 800

Min = 40 slots x 10 (average number of tickets) = 400

Probable range: somewhere inside 400-800 so lets say 500-700! (that is not a "strong" reasoning, that is just what I thought).

I guessed 400. My brain initially gave me the number 250, but then I realised the numbers in the lower rows would add up to 100's pretty quickly, so I upped it a bit.

Two rows of ten boxes at the bottom have nontrivial amounts in them, a quick eyeballing gives 30 as a possible average amount -> 600 total.

500, based on eyeballing the number of big numbers (between 15 and 20, I took 20 to adjust for the small numbers) and eyeballing the average value of the big numbers (25, I took a number slightly lower than I estimated because I knew that the 20 was probably too high). Giving the estimate 20*25=500.

500, I remember coming up with an "average nonzero cell" estimate and then multiplying it by my estimate of how many of these there were. All done in under 5 seconds, a side effect of which is that I don't really remember what process the first estimate came from.

500. Thought process was something like "there are a lot of 30s in the list, at least 3 groups of 3, so a really conservative estimate would be 300. But there are about that many boxes again having numbers in the double digits below 30. So, uh, let's go with 500."

Scans screen. 200. No, wait, that can't be right. Spots several two digit numbers which alone would add to two hundred. Looks more like . . . using previous sum as a "what 200 looks like" baseline. . . I'd say 500.

I guessed about 700, so I was way off, but on the other side. My reasoning was: the morning was pretty booked out, but most of afternoon slots (24 of them) had about 20 - 30 free. 24 * 30 = 720.

500. But it was influenced by his warning not to underestimate.

i surveyed the numbers, noticing bunches of 30-40 and few smaller numbers. so i got to roughly summing them up into hundreds.

in the end, i got to around 500. the bottom row alone gets you around 250 and the one above that another 200-250. the rest is peanuts.

i'm sure i took longer than 5 seconds for that, but 5 seconds is time i'd spend gladly on a good estimate, especially while standing in line.

500, after being primed by estimates in the article

530, really really close :o

I guessed 600.

I guessed 300.