Răspuns :
18/100×a=900
9/50×a=900
9a/50=900
9a=900×50
9a=45000
a=45000:9
a=5000
"18% dintr-un numar rational "a" " se scrie asa 18% · a sau 18:100·a
[tex]\bf 18:100\cdot a = 900[/tex]
[tex]\bf 0,18a = 900\:\:\:|:0,18[/tex]
[tex]\boxed{\bf a = 5000}[/tex]