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Mathematics: Post your doubts here!

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There are three possible no. of times a red paper clip is taken:
1) 0 times red is taken : white from box A and White from box B
2) 1 time red is taken out: Red from box A and White from Box B OR White from Box A and Red from Box B
3) 2 times red is taken out: Red from box A and Red from Box B

So first consider the 1st situation in which no red is taken out.
P(white from A and White from B) = 1/6 * 3/10 = 3/60

Now the second situation:
P(red from A and white from B OR white from A and red from B) = 5/6 * 2/10 + 1/6 * 7/10 = 17/60

Finally, the third situation:
P( red from A and red from B) = 5/6 * 8/10 = 40/60

So the probability distriburion of X is :

x | P(X = x)
0 | 3/60
1 | 17/60
2 | 40/60
 
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First we need to find the probability that a carton contains more than 1002 ml. This will be 225/900 = 0.25. Now we need to find the value of Z by working backwards from the table. Since we don't have a probability of 0.25 in the table we can find Z from (1_0.25) = 0.75. The value of Z corresponding to a probability of 0.75 is Z=0.674.
Now standardise (X >1002) ; (Z > (1002-u)/8 ) = 0.674 ; and solve
 
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There are three possible no. of times a red paper clip is taken:
1) 0 times red is taken : white from box A and White from box B
2) 1 time red is taken out: Red from box A and White from Box B OR White from Box A and Red from Box B
3) 2 times red is taken out: Red from box A and Red from Box B

So first consider the 1st situation in which no red is taken out.
P(white from A and White from B) = 1/6 * 3/10 = 3/60

Now the second situation:
P(red from A and white from B OR white from A and red from B) = 5/6 * 2/10 + 1/6 * 7/10 = 17/60

Finally, the third situation:
P( red from A and red from B) = 5/6 * 8/10 = 40/60

So the probability distriburion of X is :

x | P(X = x)
0 | 3/60
1 | 17/60
2 | 40/60
I got it. Thank you so much :D
 
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Divide this question into parts. First find all the 3 digit numbers, then find all the 4 digit numbers.

In the 3 digit numbers, the number can either start with 5 or 6 since, all the numbers must be greater than 500. If 5 is the starting number, then the ending number can be either 1 or 3 since number must be odd. If it starts with 6, then it can end with either 1, 3 or 5. The middle number can then be selected in 2C1 ways for both of the cases.
So the total number of possible 3 digit numbers are:
2 * 2C1 + 3 * 2C1 = 10

Now consider the 4 digit numbers. They can start with any number. So deal them separately:
1) 4-digit number starts with 1, so it can end with either 3, or 5. The middle 2 digits can be arranged in 2! or 2 ways. So possible arrangements: 2 * 2!
2) 4-digit number starts with 3, so it can end with either 1, or 5. The middle 2 digits can be arranged in 2! or 2 ways. So possible arrangements: 2 * 2!
3) 4-digit number starts with 5, so it can end with either 1, or 3. The middle 2 digits can be arranged in 2! or 2 ways. So possible arrangements: 2 * 2!
4) 4-digit number starts with 6, so it can end with either 1, 3, or 5. The middle 2 digits can be arranged in 2! or 2 ways. So possible arrangements: 3 * 2!

Add ^ them up to find the TOTAL possible numbers:
10 + 4 + 4 +4 + 6 = 28 numbers
 
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so for the (i) it's (3C1) (5C1 x 2C1) (3C1) = (3)(5x2) (3) =90
and for (ii) 3C1 (5C1 2C1) 3C0 + 3C1 (5C0 2C0) 3C1 + 3C0 (5C1 2C1) 3C1
and so becomes 69
but I've no idea how we got this! somebody help please :(
 
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View attachment 59961

so for the (i) it's (3C1) (5C1 x 2C1) (3C1) = (3)(5x2) (3) =90
and for (ii) 3C1 (5C1 2C1) 3C0 + 3C1 (5C0 2C0) 3C1 + 3C0 (5C1 2C1) 3C1
and so becomes 69
but I've no idea how we got this! somebody help please :(
There are 3 courses, and he can take one meal from each course. So just make selections:
Select 1 meal from the 3 meals in starter course: 3C1
Select 1 meak from 5 meals in main course. Also note that each meal is served with either new potatoes OR french fries. So you need to select any from these 2 as well. So the number of selections will become: 5C1 * 2C1
Finally select 1 meal from the Dessert course: 3C1

The total no. of possible selections can then be calculated by multiplying all the above possible selections, since these events are occuring in side by side: 3C1 * 5C1 * 2C1 * 3C1 = 90

(ii) Similarly in part (ii) you are to adapt a similar method. But now you're restricted to choosing from only courses at a time.
So you can select either Starter and Main couse, Starter and Dessert Or Main Course and Dessert.
The no. of possible selections will remain the same.

Starter + Main Course: 3C1 * 5C1 * 2C1
Starter + Dessert: 3C1 * 3C1
Main course + Dessert : 5C1 * 2C1 * 3C1

^ Sum them up to find the total possible selections. The answer will be the one you have mentioned that is 69.
 
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There are 3 courses, and he can take one meal from each course. So just make selections:
Select 1 meal from the 3 meals in starter course: 3C1
Select 1 meak from 5 meals in main course. Also note that each meal is served with either new potatoes OR french fries. So you need to select any from these 2 as well. So the number of selections will become: 5C1 * 2C1
Finally select 1 meal from the Dessert course: 3C1

The total no. of possible selections can then be calculated by multiplying all the above possible selections, since these events are occuring in side by side: 3C1 * 5C1 * 2C1 * 3C1 = 90

(ii) Similarly in part (ii) you are to adapt a similar method. But now you're restricted to choosing from only courses at a time.
So you can select either Starter and Main couse, Starter and Dessert Or Main Course and Dessert.
The no. of possible selections will remain the same.

Starter + Main Course: 3C1 * 5C1 * 2C1
Starter + Dessert: 3C1 * 3C1
Main course + Dessert : 5C1 * 2C1 * 3C1

^ Sum them up to find the total possible selections. The answer will be the one you have mentioned that is 69.
GOt that!! just needed a li'l bit of activation energy to start the topic!
 
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