Question about Extreme POTD

GRE Quant Problem Solving
1

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Here the expression simplifies to t(t-4)(t-1). Then Greg mentions that t-4 is congruent to t-1. Can someone please explain how that ‘t-4’ is congruent to ‘t-1’? Is this dealing with modular arithmetic (i.e., is he referring to mod 4)?

They seem much harder recently, not in terms of trickery, but rather testing concepts I have never seen before on the GRE. Would it be Possible to ask Greg to explain them with a bit more additional detail, like 30 sec to 1 min longer? THank you!

2

take any number t and then calculate (t-4)/3 and (t-1)/3 they have the same reminder

3

Thanks! What is this concept called? I googled “congruent numbers” and I got a bunch of modular stuff… I just don’t recall this concept from any of the amterial I have seen. Like should we remeber a list of ‘congruent’ numbers?

4

Factors, multiples and reminders
Its an application of reminder

Nope, I don’t memorise it I just follow the rules like taking an example and solving it.