Răspuns :
a,b,c,d=cifre, a diferit de zero
a>=1, 2a>=2
ab/5=(10a+b)/5=2a +b/5
abc/50=(100a+10b+c)/50=2a +b/5 +c/50
abcd/500=(1000a+100b+10c+d)/500=2a +b/5 +c/50 +d/500
2<=2a<2a +b/5<2a +b/5 +c/50<2a +b/5 +c/50 +d/500
2<ab/5<abc/50<abcd/500
a>=1, 2a>=2
ab/5=(10a+b)/5=2a +b/5
abc/50=(100a+10b+c)/50=2a +b/5 +c/50
abcd/500=(1000a+100b+10c+d)/500=2a +b/5 +c/50 +d/500
2<=2a<2a +b/5<2a +b/5 +c/50<2a +b/5 +c/50 +d/500
2<ab/5<abc/50<abcd/500