Brain Teasers
Fractional Operations
A fraction becomes 2/3 when 1 is added to both its numerator and denominator and it becomes 1/2 when 1 is subtracted from both the numerator and denominator.
Find the fraction.
Find the fraction.
Answer
The original fraction = 3/5.You can solve this fairly quickly by trial-and-error, or you can set up two equations using the information given:
1) (x+1)/(y+1) = 2/3
2) (x-1)/(y-1) = 1/2
where x is the original numerator and y is the original denominator.
First isolate x in equation 1:
x+1 = 2/3*(y+1)
x = 2/3*y-1/3
Plug this value for x into equation 2:
2/3*y - 4/3 = 1/2*(y-1)
Solve this for y to get y = 5.
Plug this value for y into equation 2 to get x = 3.
Therefore the original fraction is 3/5.
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Comments
good stuff
I quite like this teaser because of the dual explanation. It can be done by looking at 2/3=4/6=6/9 etc or by the algebra supplied. I also like Math teasers where the reasoning behind the answer is given rather than just a bald number for an answer.
I wonder if lesternoronha1 speaks any other language except Algebra!!
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