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There were twelve times more children than adults at the matinee performance of the movie .
There were 455 people at the theatre. How many adults and children were at the movie
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For your info and education:
In English, in distinction to many other languages, the phrase
"there were twelve times more children than adults . . . "
means "there were 13 times as many children as adults".
The other tutor, knowing it, simply solved the problem for you following the description that you kept in your mind
without acknowledging you.
For many people (including myself) reading emails and Internet sites is one of the sources to improve their English.
It is why I notice and inform you about your error.