四分之一×39+四分之三×25+四分之二十六×十三分之三 用简便方法计算

(1/4)*39+(3/4)*25+(26/4)*(3/13)
=1/4×39+3/4×25+26/4×3/13
=(1-3/4)×39+3/4×25+3/4×26/13
=1×39-3/4×39+3/4×25+3/4×2
=39+3/4×(25+2-39)
=39-3/4×12
=39-9
=30