Can someone please explain how this works?!?!

I

IneedHELPplease1234

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Nov 5, 2019
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I'm trying to figure out how to explain how this problem actually works. As in a way to explain what makes it work. For the life of me I just can't figure it out. It's one of those birthday math trick problems. Please help!!!

  • Add 18 to the month they were born
  • Multiply by 25
  • Subtract 333
  • Multiply by 8
  • Subtract 554
  • Divide by 2
  • Add their birth date
  • Multiply by 5
  • Add 692
  • Multiply by 20
  • Add only the last two digits of their birth year
  • Subtract 32940 to get their birthday!
 
IneedHELPplease1234 said:
I'm trying to figure out how to explain how this problem actually works. As in a way to explain what makes it work. For the life of me I just can't figure it out. It's one of those birthday math trick problems. Please help!!!

  • Add 18 to the month they were born
  • Multiply by 25
  • Subtract 333
  • Multiply by 8
  • Subtract 554
  • Divide by 2
  • Add their birth date
  • Multiply by 5
  • Add 692
  • Multiply by 20
  • Add only the last two digits of their birth year
  • Subtract 32940 to get their birthday!
Click to expand...
Please share your work/thoughts about this assignment.

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How about this trick:
Think of a number
Multiply it by 2, then by 3
Divide by 6.
You got your number. How does it work?
 
Suppose your birthday is on the x month, the yth date and in year (2 digits) 10z +w
See what happens when you plug in these variables.
You should get 10,000x + 100y + 10z+w. Do you see why. Plug real values for x, y, z and w.

Now can you figure out how to make these up?
 
Jomo said:
Suppose your birthday is on the x month, the yth date and in year (2 digits) 10z +w
See what happens when you plug in these variables.
You should get 10,000x + 100y + 10z+w. Do you see why. Plug real values for x, y, z and w.

Now can you figure out how to make these up?
Click to expand...
Ok so I tried to double check this.. The birthday I'm using is 12/07/89. My answer should be 120,789..
I took 10,000(12) + 100(07) + 10(89).. I was not sure what you meant the "w" was supposed to be so I just hit solve and got 121,590 which is already past my number without even adding anything for "w".. What am I doing wrong??
 
IneedHELPplease1234 said:
Ok so I tried to double check this.. The birthday I'm using is 12/07/89. My answer should be 120,789..
I took 10,000(12) + 100(07) + 10(89).. I was not sure what you meant the "w" was supposed to be so I just hit solve and got 121,590 which is already past my number without even adding anything for "w".. What am I doing wrong??
Click to expand...
10,000(12) + 100(07) + 10(89) is incorrect.
89 should be 10z+w:
10,000(12) + 100(07) + 10(8) + 9 = 120000 + 700 + 80 + 9 = 120789.
 
IneedHELPplease1234 said:
I just ended up getting the correct answer by using 10,000x + 100y + 1z, not 10z. 1z would be correct then?
Click to expand...
10z+w is a two digit number. Suppose you were born in 1989 so we use 89. Then z = 8 ans w=9. If instead of using 10w+z you choose to use z, that is fine. Just understand that z is a two digit number like 89. So ending up with +1z is fine because that does = 89.
 
IneedHELPplease1234 said:
I'm trying to figure out how to explain how this problem actually works. As in a way to explain what makes it work. For the life of me I just can't figure it out. It's one of those birthday math trick problems. Please help!!!
Click to expand...

  • Add 18 to the month they were born
  • if they were born in the "x"th month we have x+18

  • Multiply by 25
  • so now 25(x+ 18)= 25x+ 450

  • Subtract 333
  • 25x+ 450- 333= 25x+ 117

  • Multiply by 8
  • 8(25x+ 117)= 200x+ 936

  • Subtract 554
  • 200x+ 936- 554= 200x+ 382

  • Divide by 2
  • (200x+ 382)/2= 100x+ 191

  • Add their birth date
  • Let the birth date be "y". 100x+ 191+ y

  • Multiply by 5
  • (100x+ 191+ y)5= 500x+ 5y+ 955

  • Add 692
  • 500x+ 5y+ 955+ 592= 500x+ 5y+ 1547

  • Multiply by 20
  • 20(500x+ 5y+ 1547)= 10000x+ 100y+ 30940

  • Add only the last two digits of their birth year
  • Let that be "z" 10000x+ 100y+ z+ 30940

  • Subtract 32940 to get their birthday!
  • 10000x+ 100y+ z.
  • which is the birth date. For example, if the birth date is "Nov. 14, 1984" then z= 11, y=14, z- 84 and 10000x+ 100y+ z= 110000+ 1400+ 84= 111484.
 
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