The half-life of a certain substance is 18 years. how long will it take for a sample of this substance to decay to 63% of its original amount?

It will take 12 years to decay 63% of the substance.

Step-by-step explanation:

Given information:

The half life of substance = 18 years

Now , we know that

where,

initial mass

decay constant

time

now put the values in above equation:

As:

Now for 63% decay , we can write as:

Hence, it will take 12 years to decay 63% of the substance.

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answer: i think it is (1,-2)