Apple's Siri possesses many skills, but subtraction doesn't seem to be one of them.
Asking Siri "What's 3.23 minus 1.27?" resulted in an odd answer. Instead of responding with the correct value, Apple's voice assistant told me the current date. I tried again and got the same response. Delving further, I asked Siri to subtract a variety of other numbers with decimal points, such as "4.23 minus 1.27," "8.12 minus 3.23," "6.43 minus 2.41," and "5.25 minus 4.25." In each case, Siri answered with the current date (or in some case's the next day's date).
My wife and some of my CNET colleagues asked Siri the same initial question and got the same answer I did. I've asked Siri to subtract numbers with decimal points in the past and always got the correct response, leading me to believe this is a new glitch on the backend.
Further tests added more pieces to the puzzle. Only certain decimal point numbers seem to confuse Siri. Asking it "What is 7.87 minus 4.21?" or "What is 8.88 minus 2.41?" gets the right response. The phrasing also makes a difference. Asking Siri to "subtract 1.27 from 3.23" triggers the right answer.
Siri gets its mathematical savvy from Wolfram Alpha. But typing in the phrase "3.23-1.27" at Wolfram Alpha's Web site results in the correct answer. Those clues suggest that Siri is misinterpreting certain strings of decimal point numbers, perhaps seeing them as hours and minutes associated with a date rather than as numbers in an equation.
I reached out to Apple for comment and will update the story with any details. But for now, all of you iOS users who ask Siri to subtract certain decimal point numbers will need to phrase your question carefully. And those of you who come up with any clues to explain Siri's poor math skills are welcome to leave your comments below.