The Truth About Half-Life and Interest Rates

[thetexan]

So I'm getting ready to buy some Tritium gun sights that will glow in the dark. The advertisement says Tritium has a half life of 12.3 so the sights will be about half as bright (50%) after 12.3 years.

I'm wondering how bright they will be after 6 years and 2 months...will they be one quarter as bright?

tex

 

[PietKuip]

Simple estimate would be 75 %, but 70.7 % (square root of one half) is accurate.

 

[russ_watters]

I'm wondering how bright they will be after 6 years and 2 months...will they be one quarter as bright?

That's 1/4 LESS bright, not "as" bright.

 

[sophiecentaur]

That's 1/4 LESS bright, not "as" bright.

Yes - "Threequarters as bright".
This way of stating things is getting very common - particularly when describing the cost of things but it is potentially very confusing. It is a shame that decreases are not expressed in fractions of the original (or possibly percentage).
"Reduced to 75%" or "reduced to 3/4" of the original can't be misconstrued.
Even worse is "A hundred times less", instead of "one hundredth". This is used throughout the media and must be a nightmare for children, learning to do arithmetic. It's also a great way to hoodwink innocent consumers and voters.

 

[gmax137]

Don't get me started. My local weatherman told us this morning "It's 46 degrees now, that's twice the normal 23 degree morning temperature for December 18..."

 

[SteamKing]

Don't get me started. My local weatherman told us this morning "It's 46 degrees now, that's twice the normal 23 degree morning temperature for December 18..."

Could be worse. It could be half the normal temperature for December 18 ...

 

[sophiecentaur]

And answer me this one: then the bank manager tells you that the interest he's charging you has only gone up by 1% (i.e. from 1% to 2%) how has he the nerve not to admit that the cost has actually increased by 100%?