Puzzles for you

[i_online]

solve this puzzle:

In a country in which people only want boys, every family continues to have children until they have a boy. If they have a girl, they have another child. If they have a boy, they stop. What is the proportion of boys to girls in the country? Assume these are infinite families in the country?

From i_online

[http://neerajsingh.bizhat]

If we consider, n as the total number of families,

Then the ration of number of boys to girls will always be 2:n, where n is the number of family and n>=1

Thanks

[dsmm]

i'm sorry but i'm not very good with math(also with English)
so is his answer were right?
it's seems to be logical .
any way this is a great puzzle, do you have one that not involved with math?

[indianbaba]

nice puzzle.
Keep sharing.

[http://neerajsingh.bizhat]

Multiply of 37 by multiplies of 3:
3 x 37 = 111
6 x 37 = 222
9 x 37 = 333
12 x 37 = 444
15 x 37 = 555
18 x 37 = 666
21 x 37 = 777
24 x 37 = 888
27 x 37 = 999


Nice one:
111.111.111 x 111.111.111 =
12.345.678.987.654.321


Trapeze:

1 x 9 + 2 = 11
12 x 9 + 3 = 111
123 x 9 + 4 = 1111
1234 x 9 + 5 = 11111
12345 x 9 + 6 = 111111
123456 x 9 + 7 = 1111111
1234567 x 9 + 8 = 11111111
12345678 x 9 + 9 = 111111111
another Trapeze:

1x 8 + 1 = 9
12 x 8 + 2 = 98
123 x 8 + 3 = 987
1234 x 8 + 4 = 9876
12345 x 8 + 5 = 98765
123456 x 8 + 6 = 987654
1234567 x 8 + 7 = 9876543
12345678 x 8 + 8 = 98765432
123456789 x 8 + 9 = 987654321

and another one:

0x 9 + 8 = 8
9 x 9 + 7 = 88
98 x 9 + 6 = 888
987 x 9 + 5 = 8888
9876 x 9 + 4 = 88888
98765 x 9 + 3 = 888888
987654 x 9 + 2 = 8888888
9876543 x 9 + 1 = 88888888
98765432 x 9 + 0 = 888888888
987654321 x 9 - 1 = 8888888888
9876543210 x 9 - 2 = 88888888888

[indianbaba]

Nice puzzle.
Keep going neerajsingh.

[indianbaba]

This thread made into Sticky. If it is not updated daily it will be removed.

@i_online, in view of making this thread sticky two of your puzzles have been added here and your original posts are moved.
Cheers
indianbaba.

[http://neerajsingh.bizhat]

Thanks indianbaba for making this thread sticky. It would surely help others.

Finger Multiplication
by Sidney Kolpas
Mathematics Teacher April 2002

It requires that the students hold both hands up, with palms facing the student. The student counts his or her thumbs and fingers consecutively
from left to right, with the thumb on the left hand representing the number 1 and the thumb on the right hand representing the number 10. To multiply n times 9, where 1 <= n <= 10 and where n is a whole number, the student bends down the nth finger. The number of fingers to the left of the bent finger represents the tens-place digit of the product, whereas the number of fingers to the right of the bent finger represents the ones-place digit of the product.

The figure below illustrates 7 x 9.




Mr. Kolpas explains why this works in his article in the April 2002 issue of the Mathematics Teacher.
Courtesy : http://www.pen.k12.va.us

[indianbaba]

i never knew that.
That was something marvellous.
Keep sharing.

[http://neerajsingh.bizhat]

Finger Multiplication by Nine
by Paul Horrell
Mathematics Teacher February 2003

The "finger folding" multiplication by 9 can be expanded to include multiplicands up to 99.

The algorithm used is similar to the following:

To multiply a two-digit number by 9, 
ENTER the multiplicand by forming a V between the tens-digit finger and the next finger to its right (SPREAD). 

ENTER the units digit by FOLDing the units-digit finger.

To read the product

Hundreds digit: Count the standing fingers before the SPREAD.

Tens digit: Moving from left to right, count the fingers from the SPREAD to the FOLD; wrap around if necessary.

Units digit: Count the standing fingers to the right of the FOLD.

Example:
48x9

Enter (1 2 3 4 _ 5 6 7 F 9 0)

   Read:
   Hundreds (1 2 3 4) 4
   Tens (5 6 7) 3
   Units (9 0) 2

Example with wraparound:
83 x 9

Enter (1 2 F 4 5 6 7 8 _ 9 0)

   Read:
   Hundreds (1245 6 78) 7
   Tens (9 0 1 2) 4
   Units (45 6 7890) 7