1. 150-150*1/3=150-50=100
100+100*p/100=150
p=150-100
p=50%
2. in prima luna : 2/5*900= 360 pagini
Rest 900-360=540
a doua luna : 1/3*540=180 pagini
in a tria luna raman de citit 540-180=360 pagini
3.150+150*1/3=150+50=200 lei
200-200*p/100=150
200-150=2p
50=2p
=> p=25% este procentul reducerii