这个问题对我们来说虽然困难，但对一个数学专业的学生却易如反掌。

[误] The question, though difficult for us, is as easy as turning over his palm for a mathematics major.

[正] The question, though difficult for us, is as easy as winking for a mathematics major.

注：“易如反掌”在英语中却是“像眨眼睛一样地容易”。它们虽然表达不同，但都贴切得让人叫绝。