[Lingo] 間vs間

[steve <sjs@example.com>]

shonennhaHi all.

How does one know when 間 is pronounced あいだ and when it's ま?

I have two sentences.
This is from a short story by Haruki Murakami and according to its 
furagana it is ま.
少年は少し間を置く。
And this is from an example on the yahoo.jp dictionary for あいだ:
彼を長い間待たせておいた。

Thank you
Steve Smith