Engineers think in binary. As each binary digit is twice the...

Engineers think in binary. As each binary digit is twice the value of the preceding one (going right to left) the answer is seven binary ones (i.e. 0111 1111 arranged in nibbles, or 3F in hexadecimal) which is 1000 0000 - 1, or 2^7 -1, or 127 times by 25 rupya for each month.

So, taking the riddle at face value - a simple maths problem - we get

Total pay is (2^7-1)*25 = 127*25 = 3175 per month, so 1700/3175 months.