When can you add 2 to eleven and get 1?

on a clock
you can add 2 to 11 and get 1
except if you have a clock like this for military/overseas time:
When can you add 2 to eleven and get 1?

on a clock
you can add 2 to 11 and get 1
except if you have a clock like this for military/overseas time:
Q: Tree A and tree B both have some birds. The tree A birds tell the tree B birds “if one of you comes to our tree, our population will be the double of yours.” The tree B birds tell the tree A birds “if one of you comes here, then our population will be equal to that of yours.” How many birds in each tree?
A: Tree A has 7 birds and tree B has 5 birds
This can be done with guess and check or algebra
This is for statement 1) A + 1 = 2(B – 1)
This is for statement 2) A – 1 = B + 1
This is A in terms of B from 2) A = B + 2
Then sub into statement 1 and solve for B
B + 2 + 1 = 2B – 2
B + 3 = 2B – 2
B = 5
then can solve for A using either equation A – 1 = 5 + 1 therefore A = 7