i think "fu ta chi" equals to "二つ"("Two")
In English, we can say ,"two apples"or "two people", but in Japanese, we have to use different words though they all mean "two"
like: りんごが二つがある。(there are two apples.)
人が二人がいる。(there are two people.)
鉛筆が二本がある。(there are two pencils.)