Help with the half-life problem plesse? (chem)?

First, you have to find the half life of Nitrogen-16 which is 7.132 s. Then calculate how many half lives there are in 36 seconds. Which is 36/7.132 = approx 5. so 20/2/2/2/2/2 = 0.625 and thus in the total amount of nitrogen-16 0.625/20 is unchanged. That simplifies to 1/32.