Giải bài 3 trang 15 - SGK Toán lớp 5
Viết phân số thích hợp vào chỗ chấm:
\(a) \,\, 1dm = \, ... \,m \\ \,\,\,\,\,\,\, 3dm = \, ... \, m \\ \,\,\,\,\,\,\, 9dm = \, ... \, m\) \(b) \,\, 1g \,\,\,\,= \, ... \,kg \\ \,\,\,\,\,\,\, 8g \,\,\,= \, ... \, kg \\ \,\,\,\,\,\,\,25g = \, ... \, kg\) \(c) \,\, 1 \, \text{phút} \,\,\, = \, ... \, \text{giờ} \\ \,\,\,\,\,\,\, 6 \, \text{phút} \,\,= \, ... \, \text{giờ} \\ \,\,\,\,\,\,\,30 \, \text{phút} = \, ... \, \text{giờ}\)
Hướng dẫn:
\(10dm = 1m \\ 1dm = \, \dfrac{1}{10} \,m \\ 3dm = \, \dfrac{3}{10} \, m \)
Bài giải:
Ta có:
\(a) \,\, 1dm = \, \dfrac{1}{10} \,m \\ \,\,\,\,\,\,\, 3dm = \, \dfrac{3}{10} \, m \\ \,\,\,\,\,\,\,9dm = \, \dfrac{9}{10} \, m\)
\(b) \,\, 1g \,\,\,\,= \, \dfrac{1}{1000} \,kg \\ \,\,\,\,\,\,\, 8g \,\,\,= \, \dfrac{8}{1000} \,kg = \dfrac{1}{125} \, kg \\ \,\,\,\,\,\,\,25g = \, \dfrac{25}{1000} \,kg = \dfrac{1}{40} \, kg\)
\(c) \,\, 1 \, \text{phút} \,\,\, = \, \dfrac{1}{60} \, \text{giờ} \\ \,\,\,\,\,\,\, 6 \, \text{phút} \,\,= \, \dfrac{6}{60} \, \text{giờ} \, = \dfrac{1}{10} \, \text{giờ} \\ \,\,\,\,\,\,\,30 \, \text{phút} = \, \dfrac{30}{60} \, \text{giờ} \, = \dfrac{1}{2} \, \text{giờ}\)