Kendra says 6x65=390. Estimate to check Kendra's answer

In order to estimate the product of 6x65 in my head without writing anything down on paper or running home for my calculator, I close my eyes and I see something like this floating in space in front of me:

[6 · cos (2π) ] · e⁰ · [60 · (1Hz/1cps) ] = 360 but 65 is a little more than 60 so the product is probably a little more than 360 so 390 could be pretty close.

Hello!

There's more than one way in which to check this answer thru estimation. I'd find 6*60 and 6*70 separately, obtaining 360 and 420. It's obvious that Kendra's "390" is between 360 and 420, so it's likely that she's right.

6*65 does indeed equal 390.