yasmeen wrote:
hi... i jus don seem to grasp the concept... if any one could kindly help me out here pleaseeeeeeee...
give me basics and
explain dis prob
if 4 dice are thrown simultaneously,what is the probability tat the sum of the numbers is exactly 20
the answer goes like dis
{6,6,6,2} = 4!/3! = 4
{6,6,5,3} = 4!/ 2!
= 4
{6,6,4,4} = 4! /2!2! = 6
{6,5,5,4} = 4! / 2! = 12
{5,5,5,5} = 4!/4! = 1
ans = 35/1296
wat do these exclamatory s denote??? hz it 4!/2! 2! = 6???? please explain the whole problem
To calculate this problem, first consider the total number of ways 4 dices can be thrown. There's 6 possibilities for the first dice (1, 2, 3, 4, 5, 6), 6 possibilities for the second and so on. Therefore, there are 6x6x6x6 ways for the dices to land = 1296.
Now you need to figure out the number of ways to throw a perfect 20. {6,6,6,2} denotes a way to throw a perfect 20. To calculate the number of ways you can throw this combination of numbers, use the formula: n!/r! where r represents the number of repetitions in your group and n is the number of units. Therefore, you get 4!/3! = 4.
ie)
6.6.6.2
6.6.2.6
6.2.6.6
2.6.6.6
Do this same calculation for all your other options and you'll get 35, the total number of ways to throw 20. Put that over the total amount and you''ll find the probability.
Note: I think you made a mistake here
{6,6,5,3} = 4!/ 2!
= 4
This should equal 12 since 4!/2! = 4x3 = 12.
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