Couldn’t you lead them to guess by themselves, by asking them to guess the result of a series of expressions like:
4+2
“Hel” + “lo”
“Di” + “Caprio”
“Jack” + “Black”
“Jack” + ” Black”
“ABCD” + “EFGH”
“1234” + “5678″
Maybe insert an “ABCD” + “1234″ in between your last two expressions.
Couldn’t you lead them to guess by themselves, by asking them to guess the result of a series of expressions like:
4+2
“Hel” + “lo”
“Di” + “Caprio”
“Jack” + “Black”
“Jack” + ” Black”
“ABCD” + “EFGH”
“1234” + “5678″
Maybe insert an “ABCD” + “1234″ in between your last two expressions.