Answer: 693 years
Step-by-step explanation:
Expression for rate law for first order kinetics is given by:

k = rate constant
t = time taken for decomposition = 1
= Initial amount of the reactant
= amount of the reactant left =



for half life : 

Putting in the values , we get


Thus half life of this isotope, to the nearest year is 693.
Ok so you would just take the two fractions and simply if needed and that the answer!
Answer:
Option 2
Step-by-step explanation:
It's a rotation
Answer:
Discount = $30, Final price = $90
Step-by-step explanation:
25% is one quarter. 120/4=30
One quarter of 120 is 30, so - 30 would give discounted price of $90.
Similarly you could think of it like the discounted price is 75% of the original one and do 120x0.75=90 to find 75% of 120.
Hope this helped!