2025 袋鼠数学 B-Ecolier 真题 答案 详解

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中英双语真题

MATH KANGAROO 2025 (CHINA) - LEVEL B

3 points

1. Mia is joining small cubes, adding one at a time, to build a 3 x 3 x 3 cube. She took pictures at 5 different moments. What does Mia's third picture look like? 小米正在用小立方体搭建一个 3 x 3 x 3 的大立方体，每次添加一块小立方体。 她在五个不同的时刻拍下照片。 请问小米拍的第三张照片是什么样子？

(A)

(B)

(C)

(D)

(E)

1. Simona writes the four digits 2, 0, 2, 5 in the four boxes. Which order would give her the largest result? 小西将 2、0、2、5 四个数字填入四个方框中。 请问哪种顺序能让她得到最大的结果？ □ - □ + □ + □

(A) 5, 2, 2, 0

(B) 5, 2, 0, 2

(C) 5, 0, 2, 2

(D) 2, 2, 5, 0

(E) 2, 2, 0, 5

1. Which rope ties into a knot when the ends are pulled? 请问下面哪根绳子在两端拉紧时会打成结？ (A)

(B)

(C)

(D)

(E)

真题文字详解(英文)

Ecolier Finalized
Ecolier
3 points

1. Mia is joining small cubes, adding one at a time, to build a 3 x 3 x 3 cube. She took pictures at 5 different moments. What does Mia's third picture look like?
   (A)
   (B)
   (C)
   (D)
   (E)

Solution: While Mia builds the big cube, the numbers of small cubes becomes larger and larger. So, her photos show this order:
D, B, E, A, C
in this order. Her third picture looks like (E).

1. Simona writes the four digits 2, 0, 2, 5 in the four boxes. Which order would give her the largest result?
   □ - □ + □ + □
   (A) 5, 2, 2, 0
   (B) 5, 2, 0, 2
   (C) 5, 0, 2, 2
   (D) 2, 2, 5, 0
   (E) 2, 2, 0, 5

Solution: One of the digits is subtracted, and the other three digits are added. So, the result is the smallest when the digit that is subtracted is the largest, i.e. 5. It is also possible to calculate all five results to find the largest:
5 - 0 + 2 + 2 = 9

1. Which rope ties into a knot when the ends are pulled?
   (A)
   (B)
   (C)
   (D)
   (E)

Solution: To form a knot, the rope must create a tightening loop (one end goes under the other, then over, and then under again). This is only fulfilled by rope E.