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My PPL oral exam study guide contains this question:

If gallons-per-hour is 9.3 and time is 1 hour, 27 minutes, how many gallons will be consumed?

The book says 3.5 gallons, but im getting 13.5 gallons when I do the calculation using my E6B.

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    $\begingroup$ Voting to close as this is an inappropriate question for SE.Aviation. It's a fair question to ask of the experts, but IMHO this isn't the kind of question which passes the litmus test of "will it be useful for people 5 years from now, and so should we forever memorialize it?" Maybe @OP should bring it to the chat, instead of asking it in our Q&A. $\endgroup$ Apr 27, 2023 at 0:47
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    $\begingroup$ If there is a PPL study guide with an incorrect answer, it is possible that someone else with the same book will notice the discrepancy as well and Google it or search here, so I believe it this question is appropriate for the site. $\endgroup$
    – Someone
    Apr 27, 2023 at 3:00
  • $\begingroup$ @Someone I see your point, although I personally disagree that we should enshrine permanently every typo in every book. However, I think we can both agree that none of that information is in the question, and conclude this question doesn't meet either of our standards. $\endgroup$ Apr 27, 2023 at 12:10
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    $\begingroup$ Some very simple thinking would lead you to notice that if the aircraft uses 9.3 gallons per hour, and you fly it longer than 1 hour, it will use more than 9.3 gallons. But 3.5 is less than 9.3, so there's something wrong with the study guide. $\endgroup$
    – user253751
    Apr 27, 2023 at 22:52

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It appears that the answer in your PPL oral book is incorrect.

1 hour and 27 minutes equals 1.45 hours. Flying 1.45 hours while burning 9.3 gallons per hour means that the total fuel burned is 13.5 gallons (actually 13.485 gallons).

I would guess that the answer shown in your book as 3.5 gallons is just a typo and should read 13.5 gallons. Looks like the "1" in front of the 3.5 gallons is missing.

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    $\begingroup$ This is the answer that I got using my calculator and I wanted to be sure I was calculating correctly. Thank you for your validating my answer. $\endgroup$
    – youngpilot
    Apr 26, 2023 at 22:02
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$$ \text{1:27} = \text{1 hour} + \text{27 minutes} \cdot \frac{\text{1 hour}}{\text{60 minutes}} = \text{1.45 hours} $$

$$ \text{1.45 hours} \cdot \frac{\text{9.3 gallons}}{\text{1 hour}} = \text{13.485 gallons}$$

Your answer is correct; the book is wrong.

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1:27 is 1.45hr, times 9.3 is 13.49, so the computer is right. You should be able to guess it in your head to 13 +/- 1 (one and a half times nine). 3.5 is obviously a typo with the one missing.

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