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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