Lesson 7: Linear and Quadratic Equations. Maths Are Magic (V)
March 5, 2012How old are you?
If you ask this to your greataunt it would be indiscreet. So we are going to do it in other way …Play the following game

Now you could guess your greataunt’s age.
You will always get your greataunt’s age. Is it Magic or Maths?
Why are we always right? Could you give a logic reason?
Freely translated from Matemágicas. Descartes Project
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She thought the number 7.
by Iset Cayetano Sáez March 13, 2012 at 9:09 pmI multiplied by 8, so it’s 56.
Now I substract 130 (ten times my age) minus 56 = 74.
Witten as an equation can be: x=7·8(10·13)
There is a mistake, you must multiply by 9 instead of 8. I will give you a clue: look at nine multiplication table, it is curious isn’t it?
by mongarcia March 19, 2012 at 7:29 pmmonica it’s for you:
1.Think a number of five figures, the first and the fifth can’t be equal.
by Javier de la Torre Zapata Rabanal Ruiz Pliego Ramirez Coria Pascual March 19, 2012 at 11:58 am2.Change the first figure with the last one.(If you write 12345, now you must write 52341)
3.Now subtract the smallest number to the bigger number.(52341 – 12345 = 39996)
4.Change the first and the last figure and add it to the other number that tou get in the step number four.(69993 + 39996)
5.The number is 109989.
I will try it, I suppuse you will give me an extra point in my exam, but if you want some extra grade you have to solve my riddle about how to guess someone’s age.
by mongarcia March 19, 2012 at 7:31 pmHello Monica I did´t understand this problem at all but I think the answer is 85, Because: first I thougth in the number five and i multiplyed it by 9, then I took away this result from 10 times my age (13), so after that I have x= 13045=85
by Raúl Ortega March 19, 2012 at 5:01 pmThis can be express as : x=10·135·9 /// x=13045 /// x=85
Let x be the great aunt´s age.
by Claudia Urbina Viguera April 6, 2012 at 10:14 amThe number I thought was 7.
I am 13 years old.
FORMULA= (10·13) – (7·9) = 130 – 56 = 74 years old is the great aunt.
The age you must always use is your great aunt’s age (never your age, you are too young to have problems to tell it!)
by mongarcia April 13, 2012 at 10:17 amYou have to use your greataunt’s age! Your age doesn’t matter.
by mongarcia April 13, 2012 at 10:19 amMonica I think the problem it’s wrong because you don’t guess your greataunt’s age, but I have other way to guess it:
tell her:
by Javier de la Torre Zapata Rabanal Ruiz Pliego Ramirez Coria Pascual April 13, 2012 at 11:45 amMultiply the number 12345679 by 9.
Then multiply the answer by your age.
Finally take the first and the last numbers and you will have your greataunt’s age.
The number is 7, so 7·9=63.
by Iset Cayetano April 13, 2012 at 2:36 pmNow 14·10(ten times mi age) minus 63= 14063=77 is the granma’s age.
Written as an equation can be:
x=(10·14) 7·9
Hi Mónica.
by Irene Vides Urrestarazu April 14, 2012 at 12:19 pmMy solution:
Let x be the greataunt´s age, I thought the number 5 so if I multiply it by 9 it´s 45.
Now I substract 130, that is 10 times my age, by 45, that is 85. So my greataunt´s age is 85.
Like a fraction it could be: x= 5 · 9 – (13·10)
Mónica, when i wrote “like a fraction” is as an equation.
by Irene Vides Urrestarazu April 14, 2012 at 12:21 pmBye
Monica we are Alba and Esther and we try to do it and we can ´t we never guess our great aunt´ s age.
by Esther y Alba Navaridas April 15, 2012 at 6:09 pm