If 1/8 remains after 21 years, what is the half-life?

11.813

Explanation:

1/8 of 21 is 2.625 now you add it together which is 23.625 and half of that is 11.813

the circled areas are referred to   as sunspots.   the sunspots are cooler than the   surrounding area.

sunspots are temporary phenomena on the photosphere of the sun that appear visibly as dark spots compared to surrounding regions. they correspond to concentrations of magnetic field flux that inhibit convection and result in reduced surface temperature compared to the surrounding photosphere.

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