GRE question: Young's Double Slit Experiment

[AriAstronomer]

Homework Statement

Consider a young double slit experiments where the two slits are spaced d = 0.1mm apart. If when the screen is at a distance of l=1m the first bright maximum is displaced y = 2cm from the central maximum, then find the wavelength of the light.

Homework Equations

dsin(theta) = m(lambda)

The Attempt at a Solution

I use the small angle approximation, tanx = sinx = x = y/D.
dy/D = m(lambda), where d = 0.1mm, D = 1m, y = .02m, m=1, and I get lambda = 2000nm, but the solution manual says that the answer is 5000Angstroms. They say lambda =[ d/l ]*(dy) = [(10^-4)/2 ]*(10^-2), but I don't really see where they're getting these numbers from. Any idea?

 

[ideasrule]

Nope, but your solution is perfectly correct. The author probably screwed up and used the wrong numbers in writing the answer key.