1. 2^5*2^9 / 2^13=2^14/2^13=2; 2. 5^16*5^7/5^20=5^23/5^20=5^3=125; 3. 5^10/5^2*5^6=5^10/5^8=5^2=25; 4. 3^4*3^6/3^12=3^10/3^12=3^-2=1/9.