For the ELI5 answer:

A normal computer will compute things as True or False. So a binary 1 or a 0. This forces the computer into only accepting two possible answers for any given problem (True or False). The issue is that no matter how big or small the problem is it has to be solved using that exact same method. It just scales accordingly. Whether it's 2+2 or some calculus equation. This is very time consuming and CPUs today get around that from shear horsepower.

A quantum computer understands that not everything is solved with a True or False statement. It has the capability of engaging with more possible options right from the start. It instead says "How are all of these bits going to relate to my problem" rather than "Is this true, no, is this true, yes, is this true, no"

This might not be entirely accurate but I think it illustrates the point well enough.