SOLUTION: 8=56 7=42 6=30 5=20 3=? What does 3 equal?

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Question 777580: 8=56
7=42
6=30
5=20
3=?
What does 3 equal?

Found 8 solutions by oscargut, solver91311, tinbar, nyc_function, gurungsantosh, MathTherapy, acubed1234, mbessearch:
Answer by oscargut(2103)   (Show Source):
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3x2 = 6
I can help you with more questions at: mthman@gmail.com
Thanks

Answer by solver91311(24713)   (Show Source):
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John

Egw to Beta kai to Sigma
My calculator said it, I believe it, that settles it

Answer by tinbar(133)   (Show Source):
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The answer is 6.
Here's the pattern:
When you see "x = y" really, y = x * (x-1)
56 = 8 * 7
42 = 7 * 6
30 = 6 * 5
...
When you get to 3=? you can see it should be 3 * 2 which is 6

Answer by nyc_function(2741)   (Show Source):
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After 5 x 4 = 20, comes 4 x 3 = 12 and
then 3 x 2 = 6.

Answer by gurungsantosh(1)   (Show Source):
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56-(8+7)+1=42
42-(7+6)+1=30
30-(6+5)+1=20
20-(5+3)+1=13
answer is 13 guys

Answer by MathTherapy(10552)   (Show Source):
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8=56
7=42
6=30
5=20
3=?
What does 3 equal?

8(8 - 1) = 56
7(7 - 1) = 42
6(6 - 1) = 30
5(5 - 1) = 20
4(4 - 1) = 12
3(3 - 1) = 6

Answer by acubed1234(5)   (Show Source):
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It turns out the �?� can be whatever we want it to be!
Allow me to illustrate. Take for example, f(x)=(1/40)x^4-(13/20)x^3+(291/40)x^2-(553/20)x+42, and evaluate f(8), f(7), f(6), f(5), f(3). It turns out that:
f(8)=56,
f(7)=42,
f(6)=30,
f(5)=20,
f(3)=9.
Wait, what sorcery is this? Turns out that although the popular rule f(x)=x(x-1), which gives f(x)=6, satisfies the known values in the sequence, that f(x)=(1/40)x^4-(13/20)x^3+(291/40)x^2-(553/20)x+42 also satisfies them�except with a different value of f(3)!
Here�s another one that also works but gives f(3)=12:
f(x)=(1/20)x^4-(13/10)x^3+(271/20)x^2-(543/10)x+84
And here is one where f(3)=π
f(x)=(1/120)(π-6)x^4-(13/60)(π-6)x^3+(1/120)(251π-1386)x^2+(1/60)(3138-533π)x+14(π-6)
Finally, in general if you want the �?�=k, i.e., f(3)=k where k is the value of your choice, then
(1/120)(k-6)x^4-(13/60)(k-6)x^3+(1/120)(251k-1386)x^2+(1/60)(3138-533k)x+14(k-6)
More details here: https://www.scribd.com/doc/260182194/Elementary-Sequences
For a non-polynomial rule see here: http://i.imgur.com/BHkg0Ad.png

Answer by mbessearch(2)   (Show Source):
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The answer is 3. Equal means equals. While the various functions and formulas displayed elsewhere in answer would be reasonable if shown, without them, there are four wrong answers. One of the beauties of Math is that it is precise. Do not use equals unless you mean equals.