In a B.G. railway track, the specified ruling gradent is 1 in 250. The horizontal curve of 3° on a gradient of 1 in 250 will have the permissible gradient of A. 1 in 257 B. 1 in 357 C. 1 in 457 D. 1 in 512

The correct answer is A. 1 in 257.

The permissible gradient of a horizontal curve of 3° on a gradient of 1 in 250 is calculated using the following formula:

Permissible gradient = 1 + (3/180) * 1 in 250 = 1 + 0.005 = 1.005 in 250 = 1 in 257

The other options are incorrect because they do not take into account the angle of the horizontal curve.