The price of 100 is 2.2× 100=220 yuan.

1) If n≤220

Bought: n/2.2=5n/ 1 1 piece.

2) if n > 220

I bought: (n-220)/2+100 = n/2-10+100 = n/2-10.

2.

0.48n≠5n/ 1 1

So I bought more than 100.

0.48n=n/2- 10

0.5n-0.48n= 10

0.02n= 10

n=500