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Critical Reasoning: Assumption Questions

John talks on his home phone an average of 254 minutes a week. Jane spends, on average, 3.5 hours a week talking on her home phone. John and Jane live in the same city and all their phone calls are to local numbers. Therefore, John's phone bills must be larger on average than Jane's phone bills.

The above conclusion relies on which of the following assumptions?

Well done!

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If John made calls late at night and Jane made them during peak hours, John's bills might not be larger than Jane's after all. By jumping to the conclusion, the author of the argument assumed that the phone rates are the same at all hours, i.e. the author overlooked this matter.

Incorrect.

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Phone calls are usually charged by the minute, rather then per call, so even if this were not true, that wouldn't damage the conclusion, beause John spends more time on the phone (254 minutes is roughly 4¼ hours).

Incorrect.

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The fact John spends more time at home has nothing to do with John and Jane's phone bills and therefore does not help to explain what the author overlooked in the conclusion.

Incorrect.

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How long Jane spends on her mobile phone has nothing to do with John and Jane's phone bills and therefore does not help to explain what the author overlooked in the conclusion.

Incorrect.

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The premises provide the weekly average time John and Jane spend on their home phones, and the conclusion relates to their average phone bills. It is irrelevant how often the phone bills are calculated (even if it is monthly, annually, or daily).

John makes, on average, more phone calls a week than does Jane.
John spends more time at home than does Jane.
Jane spends no more than 30 minutes a week talking on her mobile phone.
There is no significant difference between phone call rates in different hours of the day.
Phone bills are calculated on a weekly basis.