a farmer has some pigs and some ducks.there are 9 headsand 26 feet.有猪多少
问题描述：
a farmer has some pigs and some ducks.there are 9 headsand 26 feet.有猪多少
答
有四头猪和五只羊...
列2个算式验算..
4×4+2×5=26(脚)
4+5=9(头)
答
设猪为x只,鸭y只
猪和鸭的头一共九个所以
x+y=9
猪四只脚鸭两只脚，一共26只脚，所以
4x+2y=26
解方程组得x=4,y=5
所以猪4只，鸭5只
答
四
答
猪有4只 鸭有5只