What is the correct formula to calculate the probability of this?

[Student@LinnæusUni]

what is the correct formula to use for calculating that most of 3 objects of a population of 10 is broken. 30 % that an object is broken.
Have been trying with (3/10)+(2/9)+(1/8) = 0.6472222222
the anser should be 0.650 with three decimals precision. im thinking that im missing one step but not sure which step im missing

 

[Cubist]

Welcome to freemathhelp!

You didn't use the 30% figure in your working. That should give you a strong hint.

Can you write the probability that exactly one object is broken? (9 objects will be OK)

 

[Student@LinnæusUni]

Thx, I have managed to solved it. The solution is nRc witch is 10 over 3 combination *(0,3)^3(0,7)^7 + the same values however reduce the success with 1, (3-1) untill u have 0 successes left. Then add them all together and the answer is 0.6496 with three decimals precision that will be 0.650