Question

现有1角,5角,1元硬币各十枚.从中取出15枚,共7元.1角,5角,1元硬币各取多少枚

Answer 1

x+5y+10z=70 ①

x+y+z=15 ②

x,y,z∈{0,1,2,3,4,5,6,7,8,9,10}

由①②可得,

9x+5y=80 ③

∵5y的位数必然是0或者5,

∴要使③成立,x必然为5,

∴x=5,y=7,z=3.