How many addresses can be assigned to interfaces on a /26?
Answer
62
A /26 leaves 6 host bits, so 2^6 = 64 addresses in the block, of which 62 are assignable. Two are unavailable: the all-zeros host address names the network itself and the all-ones host address is the broadcast address for it. 64 is the block size before that subtraction. 63 is the result of subtracting one instead of two, which is the most common version of this mistake. 60 has no derivation — it is what you get by rounding off, which is worth resisting in an arithmetic that is exact.