Debbie giữ bộ sưu tập đá cẩm thạch của cô trong một cái bình. Trong số 50 viên bi trong bình, 15 màu đỏ, 10 màu xanh, 20 là màu xanh lá cây và 5 là màu vàng. Debbie chọn ngẫu nhiên 30 viên bi từ jar. Bao nhiêu trong số các viên bi cô có thể mong đợi để có màu đỏ? 
Trả lời: ... hòn bi

Bản gốc : Debbie keeps her marble collection in a jar. Of the 50 marbles in the jar, 15 are red, 10 are blue, 20 are green and 5 are yellow. Debbie chooses randomly 30 marbles from the jar. How many of these marbles can she expect to be red?
Answer: ... marbles

You have 15 blue marbles. Your friend Duong takes away 3 and gives you 2. You drop 8 but pick up 4. Hung takes 4 and gives 5. You take one from Duong and give it to Hung in exchange for 3 more. You give those 3 to Duong and she gives you a blue and a yellow. Phong comes and takes the blue marbles Duong gave you and gives you a green. You give the green to Hung in exchange for a blue marble. Phong then takes a blue marble from Duong, gives it to Hung for a yellow, and gives you the yellow for a blue marble. How many green marbles do you have?

You have 15 blue marbles. Your friend Duong takes away 3 and gives you 2. You drop 8 but pick up 4. Hung takes 4 and gives 5. You take one from Duong and give it to Hung in exchange for 3 more. You give those 3 to Duong and she gives you a blue and a yellow. Phong comes and takes the blue marbles Duong gave you and gives you a green. You give the green to Hung in exchange for a blue marble. Phong then takes a blue marble from Duong, gives it to Hung for a yellow, and gives you the yellow for a blue marble. How many green marbles do you have?