Câu 1: Trang 128 sgk toán lớp 4
Tính (theo mẫu)
Mẫu: \(3+\frac{4}{5}= \frac{3}{1}+\frac{4}{5}= \frac{15}{5}+\frac{4}{5} = \frac{19}{5}\)
Ta có thể viết gọn như sau: \(3+\frac{4}{5}= \frac{15}{5}+\frac{4}{5} = \frac{19}{5}\)
a) \(3+\frac{2}{3}\) b) \(\frac{3}{4}+5\) c) \(\frac{12}{21}+2\)
Bài Làm:
a) \(3+\frac{2}{3}= \frac{3}{1}+\frac{2}{3}= \frac{3 \times 3}{1 \times 3}+\frac{2}{3}= \frac{9}{3}+\frac{2}{3}=\frac{11}{3}\)
Viết gọn : \(3+\frac{2}{3}= \frac{9}{3}+\frac{2}{3}=\frac{11}{3}\)
b) \(\frac{3}{4}+5 = \frac{3}{4}+ \frac{5}{1}= \frac{3}{4}+ \frac{5 \times 4}{1 \times 4 }=\frac{3}{4}+ \frac{20}{4}=\frac{23}{4}\)
Viết gọn: \(\frac{3}{4}+5 =\frac{3}{4}+ \frac{20}{4 }=\frac{23}{4}\)
c) \(\frac{12}{21}+2 = \frac{12}{21}+\frac{2}{1}=\frac{12}{21}+\frac{2 \times 21}{1 \times 21}= \frac{12}{21}+\frac{42}{21}=\frac{54}{21}\)
Viết gọn: \(\frac{12}{21}+2 = \frac{12}{21}+\frac{42}{21}=\frac{54}{21}\)