The 'las' in "ingeniárselas"

Question

The "las" in " … donde se las tuvieron que ingeniar …" is obviously an integral part of a specific [idiomatic?] expression; Why is it feminine plural? Is it referring to something specific? My dictionaries do list "ingeniárselas" as a separate word in its own right.

Accepted Answer

Hola David,
this is called "femenino de indeterminación"; there are set expressions that use the feminine article "la/las" referring to a non-existent reference. I don't think the origin of these expressions using la/las is known. They may come from very old expressions that maybe originally referred to something specific feminine, but thas was lost, leaving us with the expression and this unknown referent.
Here are a few examples:

ingeniárselas para... = to manage to do something, to find a solution for something
apañárselas or arreglárselas = to find a way, to cope (similar to ingeniárselas)

For example:

Mi padre tiene 89 años y vive solo, pero se las apaña bien solo. 
My dad is 89 years old and he lives on his own, but he gets by/copes.

cogerlas al vuelo = to be smart/to understand things quickly

¡Qué niño más listo! Las coge al vuelo...
What a clever boy! He gets everything...

dárselas de ... = to claim to be someone you are not/ to pretend

Susana se las daba de solidaria pero en realidad era muy egoista.
Susana claimed to be a supportive/caring person but the reality was she was very selfish.

Also with the singular "la":

tomarla con alguien/tenerla tomada con alguien = to have it in for someone

Mi profesor de inglés la tiene tomada conmigo. No sé qué le he hecho.
My English teacher has got it in for me. I don't know what I may have done.

fastidiarla = to spoil everything

Miguel, la has fastidiado. Ahora Inma no confiará más en ti.
Miguel, you ruined everything. Now Inma won't trust you again.

I hope this helped.
Saludos
Inma