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# Time dilation calculation

1. Q) the lifetime of a star is 10billion years as measured by an observer at rest with respect to the star. The star is moving away from the Earth at a speed of 0.81c.
Calculate the lifetime of the star according to an observer.

A) 17.1 billion

But plugging the numbers in to find t' I get 16.6billion. What's correct?
2. (Original post by Feynboy)
Q) the lifetime of a star is 10billion years as measured by an observer at rest with respect to the star. The star is moving away from the Earth at a speed of 0.81c.
Calculate the lifetime of the star according to an observer.

A) 17.1 billion

But plugging the numbers in to find t' I get 16.6billion. What's correct?
billion years

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