Amoeba dapat membelah diri menjadi 2 setiap 20 menit. Jika mula mula terdapat 15 amoeba maka setelah dua jam banyaknya amoeba adalah

Amoeba splits 3 times an hour. If Amoeba can split into two every 20 mins then if you divide 60 mins (which would be an hour) by 20 mins (the time they split) you would find that Amoeba can split 3 times in an hour. The question asks how many times it can split in two hours. To find this you have to multiply the 3 times 2. This means that a single Amoeba can split 6 times in two hours. There are 15 Amoeba which means if you take 15 Amoeba time 6 in two hours and 90 would be your answer. There will be 90 Amoeba after the two hours.