On: Why does the sum 7x8 catch people out?

[webhat]

Not if you remember the whole rhyme:

    Thirty days have September,
    April, June, and November.
    All the rest have 31,
    Except February alone,
    And that has 28 days clear,
    And 29 in a leap year.

[mansr → webhat]

My substitution works without contradictions there too.