Brothers and Sisters
John McCain's daughter has many sisters. She has just as many sisters as she has brothers. Each of her brothers has twice as many sisters as brothers.
How many sons and daughters, does John McCain have?
How many sons and daughters, does John McCain have?
Labels: logic, mathemagic
posted by Rajesh Lal at
8:16 AM
13 Comments:
it seams to me that there is only 2 girls and 1 guy.
quite simple realy
McCain's got 4 daughters and 3 sons.
1.) For any particular McCain daughter, she will have 3 sisters and 3 brothers. (DON'T count that daughter in -- she's the 4th girl -- otherwise it won't be 3 sisters = 3 brothers.)
2.) But for any particular McCain son, he will therefore have 4 sisters and 2 brothers. And 4 sisters are exactly twice as much as 2 brothers.
By the way, in case anyone's interested, here's the correct English grammar version of this puzzle (corrections are in ALL CAPS):
John McCain's daughter has many sisters. She has JUST as many sisters as she has brothers. Each of her BROTHERS has twice as many sisters as brothers. How many sons and daughters DOES JOHN McCAIN have?
ok Frances
this was on car talk a few months ago.. though not using John McCain's name.
The answer is 7. 4 girls and 3 boys.
each girl has 3 sisters and 3 brothres.
each boy has 2 brothers and 4 sisters.
agree with mfbabin....
2 daughters and 1 son
there is more than one answer...
they could be 2 Different johns(there are such things as like last names, u just have to be lucky to have the same frst name.
or they are Im-laws
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The true answer is in conflict with the question, Mccain has four sons, Jimmy, Andy, Dougs, & Jack, three daughters, Sidney, Bridget, and Meagan.
The answer cannot be one son as this would contradict what's in the statement. Twice as many of zero brothers is still nothing. There are therefore 3 daughters and 2 sons.
If D is the number of daughters and S the number of sons, then we know from the first statement, that
D - 1 = S
and we know from the second statement, that
S - 1 = D/2.
Insert the first equation into the second, and you get
(D - 1) - 1 = D/2 => 2(D - 2) = D => D = 4.
Insert that into the first equation, and you get
4 - 1 = S => S = 3.
So four daughters and three sons.
It is 4 daughters and 3 sons. Anything else would just not be right, I mean how can you have .4 daughters? True, if you go with decimals the answers are unlimited but for this one it has to be 4 daughters and 3 sons.
To Jen and Mo: Yup, exactly like I said earlier. The answer is 4 daughters and 3 sons. (I like Mo's elegant math explaining the answer -- so much better than my clumsy prose.)
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