Brain Teasers
Question Mark's Function Machine MKII
Question Mark has re-written the formula of his function machine. If a number goes in, a different number comes out. If:
7 -> 315
8 -> 480
9 -> 693
10 -> 960
11 -> 1287
What will come out if 20 goes in?
7 -> 315
8 -> 480
9 -> 693
10 -> 960
11 -> 1287
What will come out if 20 goes in?
Answer
7920. The formula is n^3 - n*4. In other words:7^3 (343) - 7*4 (28) = 315
8^3 (512) - 8*4 (32) = 480
9^3 (729) - 9*4 (36) = 693
10^3 (1000) - 10*4 (40) = 960
11^3 (1331) - 11*4 (44) = 1287
And therefore:
20^3 (8000) - 20*4 (80) = 7920.
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Comments
i got it right..
Glad to hear. After I submitted this, I was wondering if anyone would. Thank you and well done .
*sigh* I got this right off the bat... was very easy...
I find it easier to come up with the factors: n(n+2)(n-2)
Got it fine.
Two for two so far. Got this one on the first try, same as the first function machine. Combined time for the first two function machines is less than 30 seconds.
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