Đề bài

So sánh các phân số sau: \(\begin{array}{l}a)\frac{5}{{18}}; \frac{7}{{27}};\\b)\frac{{ - 3}}{{20}};\frac{{ - 2}}{{15}}\end{array}\)

Lời giải chi tiết

\(a)\frac{5}{{18}} = \frac{{5.3}}{{18.3}} = \frac{{15}}{{54}};\frac{7}{{27}} = \frac{{7.2}}{{27.2}} = \frac{{14}}{{54}}.\)Vì 15 > 14 nên \(\frac{{15}}{{54}} > \frac{{14}}{{54}}\) hay \(\frac{5}{{18}} > \frac{7}{{27}}\)\(b)\frac{{ - 3}}{{20}} = \frac{{( - 3).3}}{{20.3}} = \frac{{ - 9}}{{60}};\frac{{ - 2}}{{15}} = \frac{{( - 2).4}}{{15.4}} = \frac{{ - 8}}{{60}}\)Vì (-9) < (-8) nên \(\frac{{ - 9}}{{60}} < \frac{{ - 8}}{{60}}\) hay \(\frac{{ - 3}}{{20}} < \frac{{ - 2}}{{15}}\)