What's faster - brain or adding machine? You could be surprised by this information.

He was trying to figure out how much a week he will get from his annuity (annual payments) lottery win, but he only knew the $33,000 yearly amount. So I told him, immediately.

"That's $660 a week," I said confidently, almost instantly, before my friend had tried to look for the calculator app on his phone

"Whaat!" he said, "Is that right?"

He tapped away on his phone to confirm it, then looked up.

"It was $635. That's amazingly close. How did you do it so fast?"

I smiled and shrugged it off. "I'm just smart."

But the fact is there are easy tricks you can use for this kind of broad estimate.

• RELATED: How To Sell Your Lottery Annuity Payments Prize

For example, in less than a second you can tell them that getting a lottery annuity win of $100,000 per year is nearly $2,000 per week (it's $1,923, close enough).

The calculating is easy to do... here's how:

• First, just take off the 2 zeros at the end of the number. So $33,000 becomes 330.

• Then double it. This gives you 660, which is an accurate weekly amount to within a few dozen dollars.

Or, let's say you've won $100,000. And instead of spending it, you decide to put it in the bank and get 6% interest on it... $6,000 a year.

But how much is that a week?

• Take the last 2 zeros off the interest of $6,000. That leaves you with 60.

• Double it, and you get $120 per week.

The calculator says $115... but again that's close enough for a rough estimate.

There are many ways you can use this secret method to impress people. Have fun!