giúp mình giải mấy bài này nhé:
a) \(\frac{298}{719}:\left(\frac{1}{4}+\frac{1}{12}-\frac{1}{3}\right)-\frac{2011}{2012}\) b)\(\frac{27.18+27.103-120.27}{15.33+33.12}\)
2. rút gọn : B=\(\left(1-\frac{1}{2}\right).\left(1-\frac{1}{3}\right).\left(1-\frac{1}{4}\right)...\left(1-\frac{1}{20}\right)\)