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Fred is 3 years older than his sister mary, in 7 years she will be six-sevenths of his age. how old are they?

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Preliminary algebra problem really!
Let Fred and Mary be denoted by F and M respectively
Mary being x years old.
Therefore, M=x and F=x+3
In 7 years time, M=x+7 and F=x+3+7
Now, given that M is 6/7th years as old as F seven years later,
M=(6/7)(F), which becomes M=(6/7)(x+10) {EQUATION 1}
Equating EQUATION 1 with M=x+7 and solving for x gives x=11
Therefore Mary is 11 years old while Fred is 11+3, 15 years old (Seven years ago).

Posted on Jun 03, 2012

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Fred is 14 and Mary is 11

Posted on Jun 08, 2011

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Hi.

Algebra !!!!! can't stand it.

Anyway here is the answer >>>>>

Mary is 11 and Fred is 14



Regards.

Posted on Jun 08, 2011

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Fred = Mary +3
7*mary = 6/7 *Fred
substitute fred =mary + 3
7m = 6/7 * (mary + 3) 7m = 6/7*m + 6/7*3 7m - 6/7*m = 6/7*3 m(7-6/7)= 6/7*3
m = (6/7*3) / (7-6/7) m=0.419 years old
substitue m into fred = mary+3 Fred = 3.419 Years old

Posted on Jun 08, 2011

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Adjoa is three years older than her brother Kwame.seven years ago,the sum of their ages 13years.calculate the sum of their present ages.


Let Adjoa's age be x and Kwame's y.
  • Adjoa is 3 years older than Kwame: x=y+3
  • Seven years ago sum of their ages was 13: (x-7)+(y-7)=13
  • Now you substitute first equation into second equation: (y+3-7)+(y-7)=13
  • 2y-4-7=13
  • 2y=24
  • y=24/2=12 years
  • x=y+3=12+3=15 years
  • sum of their present ages is x+y=12+15=27 years

Sep 27, 2011 | Office Equipment & Supplies

1 Answer

"quadratic function" diophantus , a greek


Let x be Diophantus' age when he died.

His son died 4 years before Diophantus (so Diophantus was then x-4 years old). His son lived half as long as Diophantus so when he (son) died he was x/2.
Diophantus' son was born when Diophantus was (x-4)-x/2 years old. That was 5 years after his marriage so when Diophantus married he was (x-4)-x/2-5 years old. We also know that 1/6 of his life was spent in childhood, 1/12 in youth and 1/7 as bachelor so (x-4)-x/2-5=(1/6+1/12+1/7)x.
Now you solve last equation:
  • x-4-x/2-5=11/28x
  • x/2-11/28x=4+5
  • 3/28x=9
  • x=9*28/3=84 years

Diophantus was 84 years old when he died.

Sep 27, 2011 | Office Equipment & Supplies

2 Answers

Tom is 5 times as old as todd.In seven years Tom's age will be 6 years more than 3 times as old as Todd. How old is Todd


Todd is 4 years old.

Let Tom's age = X
Let Todd's age = Y

From the given facts:

X = 5Y

and

X + 7 + 6 = 3 ( Y + 7 )
X+13 = 3Y + 21
X = 3Y + 8

So if:
X=5Y
and
X=3Y+8

Then:
5Y=3Y+8
2Y=8
Y=4

I hope that helps.

Joe.

Sep 14, 2011 | Office Equipment & Supplies

1 Answer

Cory is 6 years older than her sister.Four years ago, she was 4 times as old her sister.how old is cory now?


let c = cory's age now let s = her sisters age now
cory's age now = sisters age + 6 years
=> c = s + 6
4 years ago, cory was 4 years younger ( i.e. c-4) and her sister was 4 years younger (s- 4)
4 years ago cory was 4 times older than her sister
=> c - 4 = 4*(s-4)
We can simplify this to c = 4s - 16 +4 c = 4s - 12
We can then use simultaneous equations to solve the two equations
(i) c = s + 6 (ii) c = 4s - 12
If we multiply both sides of equation (i) by 4 we get (iii) 4c = 4s + 24
We can then subtract equation (ii) from equation (iii) to eliminate the '4s' term => ( 4c = 4s + 24 ) - (c = 4s - 12) => 4c - c = 4s +24 - 4s +12 => 3c = 4s - 4s +36 => 3c = 36 => c = 36/3 => c = 12 => Cory's age now = 12
For clarity: Her sister's age now is of course 6 4 years ago Cory would of been 8 and her sister would of been 2
I hope this helps and good luck! If you have more questions - ask away!
Please take the time to rate this answer
Many Thanks Don.

Sep 13, 2011 | Sunburst My Mathematical Life Single...

1 Answer

Mary who is sixteen years old is four times as old as her brother.How old will mary be when his twice as old as her old brother?


Let the brother's age be x:
16years for Mary = 4x years for Brother

From equation: 4x = 16
x = 4
Therefore, the brother is 4 years old.

Mary Brother
16 4
After 4 years + 4 4
20 8
After the next 4 years + 4 4
24 12

24 is twice as old as 12; therefore for the sister to be twice as old as brother she will 24years when her brother is 12 years.

Or by calculation;

If 4 is the age for the brother, when the sister is 16, and y years will pass for the to be such that the sister is twice as old as the brother, then;

16 + y = 2(4 + y)
16 + y = 8 + 2y
16 - 8 = 2y - y
8 = y
Therefore, 8 years elapse before the sister is twice as old as the brother.

Sister will be: (16 + 8) = 24years
Brother will be: (4 + 8) = 12years

Aug 02, 2011 | Computers & Internet

1 Answer

If a 18 year old in the state of nississippi has *** with aa 17 year old will he go to jail


§ 97-3-65. Statutory rape; enhanced penalty for forcible sexual **** or statutory rape by administering certain substances. (1) The crime of statutory rape is committed when: (a) Any person seventeen (17) years of age or older has sexual **** with a child who: (i) Is at least fourteen (14) but under sixteen (16) years of age; (ii) Is thirty-six (36) or more months younger than the person; and (iii) Is not the person's spouse; or (b) A person of any age has sexual **** with a child who: (i) Is under the age of fourteen (14) years; (ii) Is twenty-four (24) or more months younger than the person; and (iii) Is not the person's spouse. (2) Neither the victim's consent nor the victim's lack of chastity is a defense to a charge of statutory rape.

Nov 09, 2010 | Health & Beauty

1 Answer

Cindy is 5 years older than Alex and 7 years older than peter sum


Three unknowns with three equasions:
cindy is 5 years older than alex. write it as c = a + 5
cindy is 7 years older than peter. write it as c = p + 7
The sum of their ages is 21. write it as c + a + p = 21
first solve for peters age in terms of alex's age.
c = p + 7 or
(a + 5) = p + 7 or
p = (a + 5) - 7 or
p = a - 2
substitute in and solve the equasion:
(a + 5) + a + (a - 2) = 21 or
3a + 3 = 21 or
3a = 24 or
a = 8

c = a + 5 or
c = 8 + 5 = 13

c = p + 7 or
p = c - 7 or
p = 13 - 7 = 6

cindy is 13, alex is 8 and peter is 6
This is called simultaneous equasions and will always work if you have the same number of unknowns as you have equasions (or relationships).

Sep 20, 2009 | Puzzle Toys

1 Answer

Find thier ages


Edwin is 14. Ruel is 7.

In 3 years Edwin will be 17. Edwin will be 10. (3*10 - 13 = 17)

Let x=Ruel's age now, and 2x=Edwin's age now.

2x+3=3(x+3)-13
2x+3=3x+9-13
2x+3=3x-4
2x+7=3x
7=x

If you are going to post these, the least you could do is rate them as Fixya. :-) Thanks!

Dec 11, 2008 | Computers & Internet

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