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đề bài
21/4 bằng bn lần 1/8
bài giải
ta có:21/4:1/8=ko có
suy ra ko có số nào thỏa mãn đề bài đã cho.
Nếu có 1 người thì sẽ hoàn thành trong số ngày là : 27 x 40 = 1080 ( ngày )
Đổi 1 tuần = 7 ngày
40 người làm 7 tuần bằng 1 người làm số ngày là :
7 x 40 = 280 ( ngày )
Sau khi làm 1 tuần thì 1 người còn phải làm là : 1080 - 280 = 800 ( ngày )
Số công nhân được giao sau 1 tuần làm việc là : 40 + 10 = 50 ( người )
Số công nhân đó làm công việc còn lại trong số ngày là : 800 : 50 = 16 ( ngày )
Đáp số : 16 ngày
\(\frac{1}{4}+\frac{1}{28}+\frac{1}{70}+\frac{1}{130}+\frac{1}{208}\)
\(=\frac{1}{1\times4}+\frac{1}{4\times7}+\frac{1}{7\times10}+\frac{1}{10\times13}+\frac{1}{13\times16}\)
\(=1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+\frac{1}{13}-\frac{1}{16}\)
\(=1-\frac{1}{16}=\frac{15}{16}\)
Chúc bạn học tốt ^^
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bài nào làm gì có cậu làm sao vậy có bài nào ko
bài nào jẬy bạn????