how many numbers of four digits greater than 2500 can be formed with the digits 0,1,2,3,4,5 and 6, if repetition is not allowed?

The first digit has five possibilities - 2, 3, 4, 5 and 6

If the first digit is 2, since the number should be greater than 2500, possibilities for second digit is 5 and 6. 

if the second digit is 5, the number of numbers possible = 5*4 = 20

if the second digit id 6, the number of numbers possible = 5*4=20

if the first digit is 3 or 4 or 5 or 6, the number of numbers possible = 6*5*4 = 120

therefore, total possible numbers which are greater than 2500 = 20+20+4*120 = 520

Hope this helps

Thanks