Bạn Trang có
đôi tất khác nhau. Sáng nay, trong tâm trạng vội vã đi thi, Trang đã lấy ngẫu nhiên
chiếc tất. Tính xác suất để trong
chiếc tất lấy ra có ít nhất một đôi tất.
A.
.
![img1](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766494156_images/obj20194219678211764766494156_img1.png)
B.
.
![img1](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766351651_images/obj20194219678211764766351651_img1.png)
C.
.
![img1](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766528083_images/obj20194219678211764766528083_img1.png)
D.
.
![img1](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766385578_images/obj20194219678211764766385578_img1.png)
Đáp án và lời giải
Đáp án:B
Lời giải:Phân tích:
Cách 1: Lấy ngẫu nhiên
chiếc tất trong
đôi tất khác nhau là
.
Số cách chọn có ít nhất một đôi tất là
.
Vậy xác suất cần tìm:
.
Cách 2: Lấy ngẫu nhiên
chiếc tất trong
đôi tất khác nhau là
.
Gọi
là biến cố:’’ Lấy bốn cái tất không thuộc đôi nào cả’’
-Lấy
đôi trong
đôi, có
cách.
-Trong
đôi lấy ra, mỗi đôi lấy một chiếc: Có
cách.
Vậy
.
Do đó:
.
Vậy đáp án đúng là B.
![img1](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766939998_images/obj20194219678211764766939998_img1.png)
![img2](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766939998_images/obj20194219678211764766939998_img2.png)
![img3](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766939998_images/obj20194219678211764766939998_img3.png)
![img4](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766939998_images/obj20194219678211764766939998_img4.png)
![img5](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766939998_images/obj20194219678211764766939998_img5.png)
![img6](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766939998_images/obj20194219678211764766939998_img6.png)
![img7](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766939998_images/obj20194219678211764766939998_img7.png)
![img8](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766939998_images/obj20194219678211764766939998_img8.png)
![img9](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766939998_images/obj20194219678211764766939998_img9.png)
![img10](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766939998_images/obj20194219678211764766939998_img10.png)
![img11](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766939998_images/obj20194219678211764766939998_img11.png)
![img12](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766939998_images/obj20194219678211764766939998_img12.png)
![img13](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766939998_images/obj20194219678211764766939998_img13.png)
![img14](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766939998_images/obj20194219678211764766939998_img14.png)
![img15](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766939998_images/obj20194219678211764766939998_img15.png)
![img16](https://cungthi.online/upload/questionbank3/eduquestion/20194219678211764766/obj20194219678211764766939998_images/obj20194219678211764766939998_img16.png)