山上的梯田形狀都不一樣，孩子跟著水牛阿牛量田地。每一題先拖捲尺，從頂點拉到底邊上，捲尺和底邊垂直才是高（斜的邊不是高）；接著切一切、拼一拼：平行四邊形沿著高剪下一個三角形，移到另一邊拼成長方形；三角形和梯形按「複製」做出一塊一樣的，轉半圈拼成平行四邊形；最後用數字鍵輸入面積。第 1 關是平行四邊形，第 2 關是銳角和直角三角形，第 3 關是梯形和鈍角三角形（高落在底邊的延長線上）。
適合年級：五年級（約 10～11 歲）。對應 108 課綱（十二年國教）數學單元：五年級「三角形、平行四邊形和梯形的面積」。各版本教科書的單元順序不同，完整對照請看國小數學課綱對照表。免費、無廣告、不用註冊，手機、平板、電腦打開就能玩，題目有注音，也會念出來。
陪玩小提醒：三個公式都是拼出來的：平行四邊形變成長方形，兩個三角形或兩個梯形拼成平行四邊形，所以要除以 2。最常見的錯誤是把斜邊當成高，可以請孩子指出「和底垂直」的那條線。
The rice terraces come in every shape, and children help Buffalo Niu measure them. For each field they first drag a measuring tape from the top vertex to the base: only a tape perpendicular to the base is the height (a slanted side is not). Then they cut and rearrange: a parallelogram is cut along the height and the triangle moved across to make a rectangle; triangles and trapezoids are copied, turned round and joined into a parallelogram. Finally they type the area. Level 1 has parallelograms, level 2 acute and right-angled triangles, level 3 trapezoids and obtuse triangles (whose height falls on the extended base).
Suits Grade 5 (about age 10–11) in Taiwan. Taiwan curriculum (12-year basic education) unit: Area of triangles, parallelograms and trapezoids (Grade 5). Free with no ads and no sign-up, in Traditional Chinese with zhuyin and in English, read aloud. See the Taiwan elementary maths curriculum map.