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Saturday, September 24, 2005
Strange numbers

In today's Straits Times Forum,
Ex-link system highly reliable

...About 4.1 million transactions are processed successfully each day, with the system achieving 99.9 per cent reliability.

Cases of wrong deductions have decreased from 0.27 per cent to 0.006 per cent from last July to July this year...

One or two cases of lost communication between driver's console and reader are reported each month...

Director, Corporate Communications, Land Transport Authority

If I didn't get this wrong, 4.1 million successful transactions and 0.006% wrong deductions implies that about 246 deductions are wrong in a day, which is more than 7000 cases in a month!

The system is 99.9% reliable, eh? That means 0.1% of unsuccessful transactions for every 4.1 million successful ones a day. That would give us about 123000 cases a month!

Strangely, only 1 or 2 cases of lost communication (lost communication can obviously be considered unsuccessful transaction) are reported. This is weird.

"Beep! Beep! Uh-oh, the machine is not reading my card! Awesome, I'll just pay cash even though it's more expensive. I just love the sound of coins!" And then the same thing happens for the next 123000 people for the entire month before one guy says "Uncle arh, your bus machine not reading my card leh!"

-- permalink --
Yiheng made
5:18 PM


Interesting stats. I wonder if they realize what you calculated. I remember reading somewhere that even though 80% chance of winning is equivalent to 20% chance of losing, people are more likely to bet on it if they hear the former.
By Anonymous Anthony, at 3:41 PM  

You raised an interesting point man. The next time an officer gives me saikang I'll tell him I only have 20% chance of completing the task without errors.
By Anonymous Yiheng, at 6:46 PM  

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