a: \(234456-123798\)
\(=230000+4456-123000-798\)
\(=107000+3658=110658\)
b: \(643546-237626\)
\(=643000+546-237000-626\)
\(=406000-80=405920\)
c: \(102078-98968+120330\)
\(=102000+78-98000-968+120000+330\)
\(=124000-560=123440\)
d: \(247122+6929-230400\)
\(=247000+6000+929+122-230000-400\)
\(=23000+651=23651\)