What is the tens digits of 7^{2011}?
7^0= 01
7^1= 07
7^2= 49
7^3= _43
7^4= _01
7^5= _07
7^6= _ 49
7^7= _43
7^8= _01
etc
Now we have the pattern 07,49,43,01, .........
2011/4 has remainder 3 so it will end in 43
