濕地的水槽旁邊有一個刻度盤，轉動它可以把水槽分成 1 到 24 等份。水面剛好落在刻度線上時會發出綠光，孩子再點水面的那條線，讀出水位是幾分之幾。第 1 關把同一個水位換成指定的等份（擴分），或換成最少的等份（約分成最簡分數）；第 2 關兩個水槽起霧了，要找到兩邊水面都對得到線的分法（通分），霧散了再比哪邊的水多；第 3 關按住水閘把兩個水槽的水放進池子，或把池子的水放一些到水桶，再讀出池子裡有多少水（異分母分數的加法和減法）。
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「約分、擴分，異分母分數的比較和加減」。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：兩個分數要找的「共同的分法」，就是兩個分母的公倍數，最小的那個最好用。可以和孩子說說看：為什麼 3 等份和 4 等份的水槽，換成 12 等份就都對得到線？
Next to the wetland tanks is a scale dial that splits them into 1 to 24 equal parts. When the water surface sits exactly on a line it glows green, and children tap that line to read the fraction. Level 1 renames one water level with a given number of parts (equivalent fractions) or with the fewest parts (simplest form). In level 2 two tanks are fogged up: children find one split that meets both surfaces (a common denominator), the fog clears, and they say which tank holds more. In level 3 they hold the gate to pour two tanks into the pond, or let some pond water out into a bucket, and read how much is in the pond (adding and subtracting unlike fractions).
Suits Grade 5 (about age 10–11) in Taiwan. Taiwan curriculum (12-year basic education) unit: Simplifying fractions; comparing, adding and subtracting unlike fractions (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.