2月18, 一战700+, Doggy, I love you!

stevehong

1. Xn= 2Xn-1 - 1,  X1=3,   then X20-X19=?
A. 2^19
B. 2^20
C. 2^21
D. 2^20-1
E. 2^21-1

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变体. X1=3, X2=5, X3=9, X4=17

X2-X1=2
Xn=2^n+1

x20=2^20+1-2^19-1
2^19*2-2^19
2^19

stevehong

2. 58 inches = 14 horse 2 inches = 14.2 horses, C has a pet with height of 15. 3 horse last year, this year it increases 3 inches, what is the height of the animal this year?
A. 15.6 houses
C 16.2 houses
选 C , reasoning: 58 inches = 14 house 2 inches, so 4 inches = 1 house, so 15.3 houses= 15*4+3 =63 inches, this year it will be 63+3=66 inches, which is 16.2 houses,
Please pay attention to A, which is not correct, since in this measurement, once it reaches 4 inches, it will add to 1 horse, "逢4进1"!!!


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机经98题变体.