Hello.
A teacher gives to a class of 10 matters and says that they will become to the examination
the 5 ones ( 5 out of 10 ) that have been occasionally chosen.
The student x has learned 7 ( 7 out of 10 ) of them. On which probability in the examination
all 5 matters are those the student x has learned?
Keyword is multiplication, I believe.
There should be 2 ways to answer the first question; right or wrong.
2*
There should be 2 ways to answer the second question; right or wrong.
2*2
Third question
2*2 *2
Fourth question
2*2 *2 *2
Fifth question
2*2 *2 *2 * 2
Sixth question
2*2 *2 *2 * 2 *2
Seventh question
2*2 *2 *2 * 2 *2 * 2
Eight question
2*2 *2 *2 * 2 *2 * 2 * 2
Ninth question
2*2 *2 *2 * 2 *2 * 2* 2 * 2
Tenth question
2*2 *2 *2 * 2 *2 * 2 * 2 * 2 * 2
I believe that probability ( it is not2^10 )
is 2^5 = 1/32. ?
first I thought that just
1/7 * 7, because it is always 1/7 ( on questions ) and there are 7 questions that student x has learned.
But it can't be like that.
So this is the best I can do ( I know
that this may be incorrect and something is possibly missing)
Maybe more multiplication is needed?
first question is 1/7
second is 1/7 x 1 /7 = 1 out of 7^2
third is 3 * 1/7 = 1 out of 7^3
fourth is 4 * 1/7 = 1 out of 7^4
fifth is 5 * 1/7 = 1 out of 7^5
sixth is 6 * 1/7 = 1 out of 7^6
seventh is 7 * 1/7 = 1 out of 7^7
The probability that the first question is one of your 7 is 7/10 (favourable cases over all possible since these are all equally likely)
Given the first question is one of the 7 the probability that the second is one of the 7 is 6/9 (one of the seven gone leaving 6 favourable cases and a total of 9)
etc.
CB
Hi. I try again.
1. 7/10 = 0,7
2. 6/9 = 0,67
3. 5/8 = 0,625
4. 4/7 = 0,57
5. 3/6 = 0,5
6. 2/5 = 0,4
7. 1/4 = 0,25
And now, I believe, we must do this;
0,7 + 0,67 + 0,625 + 0,57 + 0,5 + 0,4 + 0,25 / 7 = 9,95 %
but can this be a right probability?
Hello, stevetall!
Your grammar is strange.
I hope I interpreted the question correctly.
A teacher gives his class 10 questions says that 5 of them will be on the exam.
A student has mastered 7 of the 10 questions.
What is the probability that the student knows all 5 questions on the exam?
. .
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
An alternate approach . . .
There are: . possible exams.
The student will know all 5 questions in: . of them.
Therefore: .