Check my answer please? Probability question. Will give medal!
There are 12 red checkers and 3 black checkers in a bag. Checkers are selected one at a time, with replacement. Each time, the color of the checker is recorded. Find the probability of selecting a red checker exactly 7 times in 10 selections. Show your work.
Answer:
Well, this question is a binomial experiment so we’ll need to find the number of trials, the number of desired outcomes, and the probability of a given number of successes first.
n=10 (# of trials)
r=7 (# of desired outcomes/successes)
p=12/15 or 0.8 (probability of success in each trial)
We can then input these into the
Binomial Probability Formula: P(r successes)= nCr • pr • (1 – p)n – r
P(7 successes)= 10C7 • (0.8)7 • (1 – 0.8)10 – 7
Simplify:
P(7 successes)= 10C7 • (0.8)7 • (0.2)3
Then solve:
We’ll first solve the combination at the beginning of the equation by using the combination formula: n!/r!(n – r)!
10C7 inputted into the formula: 10!/(10 – 7)! = 10!/3! = 10 • 9 • 8 • 7 • 6 • 5 • 4 • 3 • 2 • 1
–––––––––––––––––––––––––
3 • 2 • 1
10 • 9 • 8 • 7 • 6 • 5 • 4 • 3 • 2 • 1
–––––––––––––––––––––––––
3 • 2 • 1
10 • 9 • 8 • 7 • 6 • 5 • 4 = 604,800
Then put that into the original equation:
P(7 successes)= 604,800 • (0.8)7 • (0.2)3
And solve for the exponents next:
P(7 successes)= 604,800 • (0.2097152) • (0.008)
Then to finish:
P(7 successes)= 604,800 • (0.0016777216) = 1014.68602368 OR 1014.68 (rounded)
1014.68 is our final answer.

Question

Check my answer please? Probability question. Will give medal!
There are 12 red checkers and 3 black checkers in a bag. Checkers are selected one at a time, with replacement. Each time, the color of the checker is recorded. Find the probability of selecting a red checker exactly 7 times in 10 selections. Show your work.
Answer:
Well, this question is a binomial experiment so we’ll need to find the number of trials, the number of desired outcomes, and the probability of a given number of successes first.
n=10 (# of trials)
r=7 (# of desired outcomes/successes)
p=12/15 or 0.8 (probability of success in each trial)
We can then input these into the 
Binomial Probability Formula: P(r successes)= nCr • pr • (1 – p)n – r
P(7 successes)= 10C7 • (0.8)7 • (1 – 0.8)10 – 7
Simplify:
P(7 successes)= 10C7 • (0.8)7 • (0.2)3
Then solve:
We’ll first solve the combination at the beginning of the equation by using the combination formula: n!/r!(n – r)!
10C7 inputted into the formula: 10!/(10 – 7)! = 10!/3! = 10 • 9 • 8 • 7 • 6 • 5 • 4 • 3 • 2 • 1
                                                                                     –––––––––––––––––––––––––
                                                                                                         3 • 2 • 1 
10 • 9 • 8 • 7 • 6 • 5 • 4 • 3 • 2 • 1
 –––––––––––––––––––––––––
                   3 • 2 • 1 
10 • 9 • 8 • 7 • 6 • 5 • 4 = 604,800 
Then put that into the original equation:
P(7 successes)= 604,800 • (0.8)7 • (0.2)3
And solve for the exponents next:
P(7 successes)= 604,800 • (0.2097152) • (0.008) 
Then to finish:
P(7 successes)= 604,800 • (0.0016777216) = 1014.68602368 OR 1014.68 (rounded)
1014.68 is our final answer.

ganeshie8 · Answer

procedure is correct,
but there must be a mistake in ur calculation for sure

zzr0ck3r · Answer

best answer $\downarrow$

ganeshie8 · Answer

how can i say that wid confidence ? 
cuz you got probability = 1014.68... which is impossible....  

probability is always between <=1 and >=0

ganeshie8 · Answer

check ur  10C7 calculation again

anonymous · Answer

Oh! I forgot the r! before the (n - r)! Didn't I?

ganeshie8 · Answer

BINGO !

anonymous · Answer

I knew I must have done something wrong. Thank you so much for helping me fix my mistake! I really appreciate it! :)

ganeshie8 · Answer

np :) u can use wolfram as ur calculator : http://www.wolframalpha.com/input/?i=%2810+choose+7%29+*++%280.8%29%5E7+*+%281+%E2%80%93+0.8%29%5E%2810+%E2%80%93+7%29

ganeshie8 · Answer

it is the best in free online calculator business

ganeshie8 · Answer

btw, (10 choose 7)  is same as   10C7