help please

Question

there are 300 secondary 4 students at a secondary school and 40% of them have bicycles. of the remaining grades (secondary 1,2,3), only 10% of them have bicycles. if 15% of all the students have bicycles, how many students are in those of other grades?

Answer 1

40%*300=120

120+10%(x)=15%(300+x) where x=total number of secondary 1,2,3 students

120+0.1x=0.15(300+x)

120+0.1x=45+0.15x

120-45=0.15x-0.10x

75=0.05x

7500=5x

x=7500/5

x=1500 secondary 1,2,3 students

check:

1500+300=1800

15%*1800=270

10%*1500=150, 40%*300=120, 150+120=270