Radon-219 has a half-life of about 4 s. After 20 s, how many milligrams of a 500 mg sample will remain?

435.3 mg

211.6 mg

31.3 mg

15.6 mg

Help please I’ll make you the brainliest if right

2people are trying different phones to see which one has the better talk time. chatlong has an average of 18 hours with a standard deviation of 2 hours and talk-a-lot has an average of 20 hours with a standard deviation of 3. the two people who tested their phones both got 20 hours of use on their phones. for the z-scores i got 1 for the chatlong company and 0 for talk-a-lot. what is the percentile for each z-score?

Kai walked one and two-thirds of a mile on saturday and four and one-sixth of a mile on sunday. how many miles did kai walk?

Yvaries directly as x. y =90 when x=6. find y when x=13