How exactly would you go about this problem

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1

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<p>I solved it using a method that would take ages, but its there a really quick and easy way to solve this?</p>

2

<p>So I’ve thought of a different method of doing it which is just figuring out numbers for a and b that would make sense here</p>

<p>Since we have [5,a,b,5] then since a<0 it would only be logical to make a = -1 and thus
b = -5. </p>

<p>From there I just wrote out the sequence</p>

<p>5, -1 , -5, 5, -5^2, -5^3, 5^5, -5^8, -5^13, 5^21</p>

3

<p>Hard to say, but it took me a lil time to do this one. Easiest way is to write out all the terms to the 10th but more pattern wise:</p>

<p>5a = b
ab = 5
a*5a = 5 , so a^2 = 1, a = ± 1, and it says a < 0, a = -1</p>

<p>After doing a few terms, you will see -5 * 5 = 5^2, 5^2*5^1 = 5^3 * 5^2 = 5^5…</p>

<p>looking at the exponents, 1,1,2,3,5,8… </p>

<p>The exponents follow Fibonacci’s sequence. :D. The charge of the number goes +,-,-,+.</p>

<p>note, the only reason why I even looked at the exponents is because the answers had exponents :D</p>

4

<p>Lol I wrote out those first two equations (5a=b, ab=5), but I didn’t even bother to solve them because I didn’t reason it would go anywhere. But yeah, I think that its doable in under a minute using the method of writing out the 10 terms</p>

5

<p>^Yea, the math SAT just do stupid things, giving random info. The only way I see doing most of the SAT questions is by just randomly testing out what they give me. I swear that the SAT just tests who can do the most trial and error. There’s problems that force you to even try the answers, I mean seriously ***. The SAT ppl should learn from the ACT or something-- that’s what I think; I despise the SAT.</p>

<p>Took me like a minute for the pattern, but I forgot the negative sign and I counted incorrectly (looked for 5^34, 'cause that’s the 11th, but I thought it was the 10th) so it took like 3 minutes instead. -.-</p>

6

<p>seems u can use a factorial, since u need to multiply it all anyway.</p>

7

<p>I don’t think a factorial works because you only mutiply the last 2 digits. It’s doing Fibonacci’s sequence with the exponents.</p>