The answer in the book is WRONG ... I think. Basic maths question

[MathsFormula]

The question is:

Lady makes 30 cakes every hour.
How long does it take her to make 220 cakes?
Give your answer in hours and minutes.

Answer in book is 7 hours and 10 minutes


I think this is incorrect. I think the answer should be 1 hour and 19 mins

My calculation:

220/30 = time to make 30 cakes = 7.33 hours. 0.33 hours is 19 mins [0.33 x 60 mins]

So my answer is 7 hours and 19 mins.

Please advise if I'm wrong and why. Thank you.

 

[Quaid]

The question is:

Lady makes 30 cakes every hour.
How long does it take her to make 220 cakes?

Answer in book is 7 hours and 10 minutes

I think the answer should be 1 hour and 19 mins

0.33 hours is 19 mins [0.33 x 60 mins]

my answer is 7 hours and 19 mins

Hi there. Yes, the book answer is not correct. (You also made a typo, by the way, highlighted in red above.)

Although your answer is better, it has round-off error.

0.33*60 = 19.8

You need to round this result to the nearest minute.

Another way to look at the decimal approximation is to realize the following.

0.3333... (where the ellipsis dots indicate that the 3s continue forever) is equal to 1/3.

1/3 of an hour is 60/3 minutes. How many minutes is that?

Cheers :cool:

PS: All math texts contain errors.

 

[MathsFormula]

Thanks for the replies

 

[Deleted member 4993]

The question is:

Lady makes 30 cakes every hour.
How long does it take her to make 220 cakes?
Give your answer in hours and minutes.

Answer in book is 7 hours and 10 minutes


I think this is incorrect. I think the answer should be 1 hour and 19 mins

My calculation:

220/30 = time to make 30 cakes = 7.33 hours. 0.33 hours is 19 mins [0.33 x 60 mins]

So my answer is 7 hours and 19 mins.

Please advise if I'm wrong and why. Thank you.

If you were to make 215 cakes - the book answer would have been correct!

 

[HallsofIvy]

If she makes 30 cakes per hour and must make 220 cakes, it will require 220/30 hours. Now 220/30= 7 with remainder 10. Perhaps whoever did the answer in the book (typically not the author) mistook that remainder for "minutes". In fact, it is 10 cakes still left to cook after 7 hours. 10/30= 1/3 of an hour which is 60/3= 20 minutes, not 10 minutes.