| Author | Primary school questions |
|---|
for blazingarpit:
Uranus (the only other planet) also has retrograde motion. |
| In a two-child family, one child is a boy. What is the probability that the other child is a girl? |
| 50-50 |
| Sorry, incorrect. Try again. :) |
In a two-child family, one child is a boy. What is the probability that the other child is a girl?
For the first child it was 50% chance. For the second child also 50% chance.
50+(100-50):2= 75
So i think 75% chance :P |
| Wrong again. But warmer. :) |
50-50
#25 said 75%...so 15%,35%,45%
since its not 50% and could be 80% only guessing tho. |
| 0% and 100%? |
The answer is . . .
2/3 = ~66%
There are 4 outcomes each with equal chance.
A.) Boy Girl
B.) Boy Boy
C.) Girl Boy
D.) Girl Girl
Since it is already stated that there is at least 1 boy, then outcome D isn't possible. This leaves us with only 3 possible outcomes. The chance of A or C happening is 1/3 + 1/3 = 2/3. |
#22
Dad chromosomes { X, Y }
Mom chromosomes { X, X }
So we have cartesian product of the parents chromosomes:
{ X, Y } * { X, X } = { (X,X), (X,X), (Y,X), (Y,X) }
Obviously, 50% boy and 50% girl, considering the parents are normal and ignoring other factors.
No matter how many kids the family already has, boys or girls, each new born still has a 50:50 chance to be boy or girl. |
#29
I don't get it. Admittedly Maths is not my strong point, but how is C) a possibility if there is already a boy? Surely only A) and B) are possible?
If there were originally 4 possibilities, then 1/4 + 1/4 = 1/2.
As I said I'm not good at maths so I would love to understand this probability question - I'm a primary school teacher too! Good thing I only teach grade 1 :))) |
#29
When you flip two coins, you have 4 equal chances of having:
a) head head
b) head tail
c) tail head
d) tail tail
If we already flip one coin, let's say it's head, then the chances of the other coin being tail would be 66%? I strongly think it still has a 50% chance to be either head or tail.
Think about the rabbit and turtle paradox. Not all problems have their answers in math. |
#31, #32
You have to read it more carefully. :)
In a two-child family, one child is a boy. What is the probability that the other child is a girl?
It says "one child is a boy". It never said the first child was a boy.
For this problem you need both math and the ability to read tricky problems. I put this one together because previous problems required one or the other ability.
Here's a purely math problem:
Which is more: being given one million dollars, or one penny the first day, double that penny the next day, then double the previous day's pennies and so on for a month? |
#33
aaaahh ok. thanks for the clarification. It all seems so simple now lol!
It was a good problem Pantheon. |
| #33 2^30 pennies = 1 073 741 824 pennies = ~ 1 073 742 dollars > 1 000 000 dollars |
I think for the boy/ girl thing it comes down to the wod - is a girl, rather than was a firl.
At the point of birth the probability was 50:50 for it to be a girl. But the question is refering to the arrangement of 1 of each.
For #33 give me a penny a day probably.
I haven't bothered to calculate 2^30. And I would defniately make sure I did it on a month of 31 days!!
Same as teh grains of rice on a chess board thing. |
#34
Thanks. I found it online and thought it was perfect. :)
#35, #36
Formula is 2^n-1. n=days
You are correct that pennies are better. DarkSooth, you are still right, but there are only 100 pennies in 1 dollar; not 1000 pennies. :)
Next question:
DarkSooth is twice as old as MilesTeg. Three years from now, the sum of their ages will be 42. How old is DarkSooth? |
| 26? |
DarkSooth is twice as old as MilesTeg. Three years from now, the sum of their ages will be 42. How old is DarkSooth?
26 is a usual answer but its wrong!!!
"3" years from now after 2 x their ages.
so what x 2 = 42? = 26 + 3 years = 29.:P |
D=2M
D+M+6 = 42
combining simultaneous equations
1.5D+6 = 42
1.5D = 36
D= 24
Or alternatively
Miles Teg is 28 years old (coz I am)
Therefore Dark Sooth is 56!!! |
