World-famous engineer John Johnson decided to take a break from his latest invention, and asked his wife if she had any chores he could do to clear his mind. She handed him a grocery list and told him to go to the store. The list contained perfectly ordinary items such as bread and yogurt, as well as batteries.

When John got home, his wife was surprised and perplexed to see that he had purchased a total of 170 batteries.

"Why did you buy so many batteries?" she asked.

John answered "I just bought the number on the list."

Perplexed, she looked at the list just to make sure and told him "I didn't even put a number here at all."

Why did John buy so many batteries?

  • 18
    $\begingroup$ This would make a bit more sense if JJ were a world-famous software or computer engineer, as other types of engineering have much less use for the important facts of this question. $\endgroup$ May 2, 2016 at 17:39
  • 10
    $\begingroup$ Because his kids keep taking them out of the remote $\endgroup$
    – user11791
    May 2, 2016 at 21:37
  • $\begingroup$ John Johnson should be Jon Skeet :P $\endgroup$
    – palsch
    Jun 11, 2016 at 6:26

2 Answers 2


He did this because

170 in hex is AA. She asked for "Double A" batteries.

  • 26
    $\begingroup$ at least she didn't ask for the next size down... $\endgroup$ May 2, 2016 at 14:09
  • 19
    $\begingroup$ Wait, did she write 0xAA batteries? Otherwise it stretches the suspension of disbelief. $\endgroup$
    – vsz
    May 2, 2016 at 15:40
  • 6
    $\begingroup$ AA implies at least base 11 (since the standard decimal digits suffice for bases 2-10). Base 16 is arguably the most commonly used base that requires additional symbols for transcription. $\endgroup$ May 2, 2016 at 16:38
  • 5
    $\begingroup$ The question remains - what size batteries did he buy? Since she didn't specify (at least by his interpretation), it's quite likely they're all the wrong type... $\endgroup$ May 2, 2016 at 18:11
  • 16
    $\begingroup$ @DarrelHoffman Car batteries. $\endgroup$
    – Devsman
    May 2, 2016 at 18:23

The list said

"While you are at the store, if they have batteries, buy a pack." He looped until he bought the store's entire stock of 170.

  • 3
    $\begingroup$ Like the old one about the computer programmer who was found dead in his shower with hundreds of empty shampoo bottles - "Lather; rinse; repeat" $\endgroup$
    – RDFozz
    Apr 23, 2018 at 21:09

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