How can the wavelength of blue light be 750nm?

[FaroukYasser]

Homework Statement

A Visible light is shone on a diffraction grating. Two rays are produced, One Orange ray with 600 nm which is at the fifth order maxima. It coincides with a blue ray at the fourth order maxima. Find the wavelength of the blue light.

Homework Equations

n x lamda = dsin(theta)
where n = number of order
lamda = wavelength

The Attempt at a Solution

Basically what I did was say that (d) was constant since it was the same diffraction grating. and the same Sin(theta) since they occurred and coincides at the same point so dsin(theta) is the same for both, Then I did:
For orange light:
5 x 600 x 10^-9 = dsin(theta) (1)*
For blue light:
4 x Wavelength of blue light = (1)*
4 x lamda = 5 x 600 x 10^-9
lamda = 750 nano meters!
How can the wavelength of blue light be 750 nm! This is the wavelength of red light!
Is there a mistake in the question?
Thanks.

 

[ehild]

Is there a mistake in the question?

Certainly, they did. Perhaps mixed 4 and 5.

ehild

 

[FaroukYasser]

Thanks. That's a relief. Spent almost an hour trying to figure out if there was any other possible way to solve it. Thanks a lot