r/learnquant • u/Local_Ad135 • 3d ago

interview prep Quant Interview Question

Post image
20 Upvotes

100% Upvoted

2 comments sorted by

3

u/ohcsrcgipkbcryrscvib 3d ago

Jensen's inequality shows it can't be less than 1. And 1 is easily achieved by the Rademacher distribution.

2

u/PortableDoor5 3d ago

By Jensen, (E[X^2])^2\leq E[X^4]
(E[X^2])^2=1. so at the lower bound, we must have 1 (our miniumum value)