Question 1053736: If I multiply my age when I was 20 years younger with my age when I am 6 years older I get 5760 how old am I?
Found 2 solutions by ankor@dixie-net.com, KMST:
Answer by ankor@dixie-net.com(22740)   (Show Source):
You can put this solution on YOUR website! If I multiply my age (a) when I was 20 years younger with my age when I am 6 years older I get 5760 how old am I?
:
(a-20)*(a+6) = 5760
FOIL
a^2 + 6a - 20a - 120 = 5760
a^2 - 14a - 120 - 5760 = 0
a^2 - 14a - 5800 = 0
You can use the quadratic formula to solve this, but it will factor to
(a-84)(a+70) = 0
the positive solution
a = 84 is your present age
:
:
See if that checks out
64 * 90 = 5760
Answer by KMST(5328)  (Show Source):
You can put this solution on YOUR website! Another way:
 so  has
 factors,
forming  pairs.
We could list them all, starting with
 and so on.
However, we are looking for a
 product
of two factors that are
 units apart.
Our product would be towards the end of the list.
Since is between
 and  ,
and neither  nor 
is a factor 76of ,
we are looking for factors
 and  .
Obviously, 77, 78, and 79
are not factors of 5760,
but  is.
Likewise, it is easy to see that
81, 82, ....88, and 89 are not factors,
but  is.
That gives us two pairs:
 so 
would be the last pair in the list,
and  so 
is the second to last pair.
It is also the pair we want, because
 .
So,  --->  .
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