Two grandparents want to pick up the mess that their granddaughter had made in her playroom. one can do it in 15 minutes working alone. the other, working alone, can clean it in 12 minutes. how long will it take them if they work together?

  6 2/3 minutes

Step-by-step explanation:

Their rates in "jobs per hour" are ...

  (60 min/h)/(15 min/job) = 4 jobs/h

and

  (60 min/h)/(12 min/job) = 5 jobs/h

So, their combined rate is ...

  (4 jobs/h) + (5 jobs/h) = 9 jobs/h

The time required (in minutes) is ...

  (60 min/h)/(9 jobs/h) = (60/9) min = 6 2/3 min

Working together, it will take them 6 2/3 minutes.

the answer is: d) o, f, and kr.

atomic radius of bromine (br) is 114 pm.

atomic radius of oxygen (o) is 73 pm.

atomic radius of fluorine (f) is 72 pm.

atomic radius of krypron (kr) is 112 pm.

the atomic radius of a chemical element is a measure of the size of its atom.

the atomic radius varies with increasing atomic number, but usually increases because of increasing of number of electrons.

the atomic radius decreases across the periods because an increasing number of protons, because greater attraction between the protons and electrons.