The rate constant for this first-order reaction is 0.710 s1 at 400 C.

A-> Products

How long (in seconds) would it take for the concentration of A to decrease from 0.820 M to 0.290 M?

1.016 seconds

Explanation:

Let's bring out the parameters we were given in the question;

Rate constant k  = 0.710 s^-1

Initial Concentration [A] = 0.820 M

Final concentration [A]o = 0.290 M

Time t = ?

Formular relating these parameters is given as;

ln[A] = ln[A]o − kt

Making t subject of interest, we have;

ln[A] - ln[A]o = -kt

kt = ln[A]o - ln[A]

t = (ln[A]o - ln[A]) / k

Substituting the values, we have;

t = ( ln(0.820) - ln(0.290) ) / 0.710

t = 0.7217 / 0.710

t = 1.016 seconds

8 m/s because for him to get the same amount of energy as ray is putting out, bobby, who weighs half as much as ray, needs to run twice as fast.

i think   the answer is c hope i'm right