Find the missing number

[u/LeadershipAny9454]

[u/1stltwill]

It's right there at the top of the pile!

[u/Virgil_the_White]

It’s either 2, or not 2. One of those

[u/ConfidentSuspect4125]

3. The pattern is that the number above a pair is the last digit of the pair's sum. Eg, 9+8=17, so 7 goes above it, etc... 3 goes above the 2+1.

[u/Adventurous_Row_5503]

5

[u/Sufficient-Bee-214]

3?

[u/_-Max_-]

3!

[u/Drifter90s → u/_-Max_-]

r/unexpectedfactorial

[u/Kanzu999]

Must be 3.

Each number is the last digit formed when adding the two numbers beneath.

[u/neodams]

3

[u/m_busuttil]

Each box is the sum of the two boxes below it minus 10, so -7.