Collins Chinese Dictionary Plus (3rd edition), 2011:
吹灰之力 chuī huī zhī lì 名
little effort
- 他不费(費)吹灰之力就通过(過)了考试(試)。 Tā bù fèi chuī huī zhī lì jiù tōngguòle kǎoshì. He got through the exam with very little effort.