直接寫的數字。15× 6 = 510-51 = 25× 40 = 121+69 = 415+715 = 79-29 =

510-51=459

25×40=1000121+69=190415+715=111579-29=591-111=101165438 +07+27+47=110+10÷2=15120-39-21=6096×23≈20003105÷15≈200