Half Life, radioactive isotope?

Question

For 1.4 mole of the radioactive isotope xenon-133, half-life = 5.3 days, how many disintegrations have occurred after 20 minutes?

Hint:
Think about what disintegrates - a single isotope.
How many isotopes are there in the amount of moles given ?
How many disintegrated is the difference between initial and final number of isotopes


I know one would use the following formula/procedure:
[A]t = [A]0*e^(ln2*t/t 12) to find [A]t.

Then,

[A]0 - [A]t = x.

Finally,

x * 6.022e23.


Though, I can't seem to figure out the correct answer.

Last Answer: 1.53137e31
Incorrect, tries 2/12.

any *help* would be deeply appreciated.

Answer 1

1.5 x 10^21

Not 10^31