Reduce challenge - Where did ‘add’ come from?

Just started the ‘reduce()’ challenge task and on step 4 it says to use ‘(and add)’. I figured it out after searching the community answers.

But I still can’t find where ‘add’ is referenced in the videos before? Was it from a long ways back or was I supposed to just go search ‘add’ to figure it out somehow.

It feels a little like we didn’t talk about it in the video, but hey use this!

I’m sure it’s me that’s missed it because it was talked about way back, but I have searched and can’t find it in the previous lessons.

It sure would be useful to make reference to previous videos when doing this sort of thing. I get that we need to learn to figure stuff out, but a link to a video that might contain something useful in overcoming a code challenge, would be super helpful. :)

from operator import add
from functools import reduce

prices = [
    (6.99, 5),
    (2.94, 15),
    (156.99, 2),
    (99.99, 4),
    (1.82, 102)
]

def product_sales(tpl):
    return tpl[0] * tpl[1]

total = reduce(add, map(product_sales, prices))