AMC8 2023
AMC8 2023 · Q18
AMC8 2023 · Q18. It mainly tests Linear equations, Diophantine equations (integer solutions).
Greta Grasshopper sits on a long line of lily pads in a pond. From any lily pad, Greta can jump $5$ pads to the right or $3$ pads to the left. What is the fewest number of jumps Greta must make to reach the lily pad located $2023$ pads to the right of her starting position?
绿草hopper Greta 坐在池塘中一长排睡莲上。从任何睡莲上,Greta 可以向右跳 $5$ 个睡莲或向左跳 $3$ 个睡莲。Greta 到达起始位置右侧 $2023$ 个睡莲的位置需要的最少跳跃次数是多少?
(A)
405
405
(B)
407
407
(C)
409
409
(D)
411
411
(E)
413
413
Answer
Correct choice: (D)
正确答案:(D)
Solution
We have $2$ directions going $5$ right or $3$ left. We can assign a variable to each of these directions. We can call going right $1$ direction $\text{X}$ and we can call going $1$ left $\text{Y}$. We can build an equation of $5\text{X}-3\text{Y}=2023$, where we have to limit the number of moves we do. We can do this by making more of our moves the $5$ move turn than the $3$ move turn. The first obvious step is to go some amount of moves in the right direction then subtract off in the left direction to land on $2023$. The least amount of $3$’s added to $2023$ to make a multiple of $5$ is $4$ as $2023 + 4(3) = 2035$. So now, we have solved the problem as we just go $\frac{2035}{5} = 407$ hops right, and just do 4 more hops left. Yielding $407 + 4 = \boxed{\textbf{(D)}\ 411}$ as our answer.
我们有两个方向:向右 $5$ 或向左 $3$。我们可以为每个方向分配一个变量。我们称向右为 $1$ 方向 $\text{X}$,向左 $1$ 为 $\text{Y}$。我们可以建立方程 $5\text{X}-3\text{Y}=2023$,同时要限制移动次数。我们可以通过让 $5$ 的移动次数多于 $3$ 的移动次数来做到这一点。第一步显然是向右做一些移动,然后向左减去以落在 $2023$ 上。将 $4$ 个 $3$ 加到 $2023$ 上使其成为 $5$ 的倍数是最少的,因为 $2023 + 4(3) = 2035$。因此,我们现在解决了问题:向右跳 $\frac{2035}{5} = 407$ 次,向左跳 $4$ 次。总共 $407 + 4 = \boxed{\textbf{(D)}\ 411}$ 次。
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