事倍功半

twice the effort for half the result

matter / thing / item / work / affair / CL:件[jian4],樁|桩[zhuang1],回[hui2]

(two, three etc) -fold / times (multiplier) / double / to increase or multiply

meritorious deed or service / achievement / result / service / accomplishment / work (physics)

half / semi- / incomplete / (after a number) and a half