Why does the phrase なんでレポートをおくりましたか have 2 kinds of meaning according to my textbook

Question

なんでレポートをおくりましたか can mean:

1. What did you send the report by (I send the report by fax according to my textbook) or
2. Why did you send the report (according to google translate)

Answer 1

なんで is an informal interrogative that normally means the same thing as どうして ("why"), so Google's translation is the natural interpretation of that sentence. However, as this dictionary entry explains, なんで sometimes means the same thing as なにで ("how; by what means"), too.

Since this can be confusing even to native speakers, in reality, なんで does not mean "by what means" very often. To say "by what means", なにで is preferred most of the time.

• なんでそこへ行くの？
  Why do you go there? (Usual interpretation)
  How do you go there? (Uncommon interpretation)
• なにでそこへ行くの？
  (= どうやってそこへ行くの？)
  How do you go there? (By bus? By train?)