Đáp án:
Giải thích các bước giải:
A=$\dfrac{2}{5}+$ $(-\dfrac{4}{3})+$ $(-\dfrac{1}{2})$
=$\dfrac{2}{5}$ $-\dfrac{4}{3}$ $-\dfrac{1}{2}$
=$\dfrac{12}{30}$ $-\dfrac{40}{30}$ $-\dfrac{15}{30}$
=$\dfrac{12-40-15}{40}$
=$-\dfrac{43}{30}$
b,
B=$\dfrac{1}{3}- [$$(-\dfrac{5}{4})-($ $\dfrac{1}{4}+$ $\dfrac{3}{8}$)]
=$\dfrac{1}{3}- [$($-\dfrac{5}{4})-($ $\dfrac{2}{8}+$ $\dfrac{3}{8}$)]
=$\dfrac{1}{3}- ($$-\dfrac{10}{8}-$ $\dfrac{5}{8}$)
=$\dfrac{1}{3}- ($$-\dfrac{15}{8}$)
=$\dfrac{1}{3} $$+\dfrac{15}{8}$)
=$\dfrac{8+45}{24}$
=$\dfrac{53}{24}$
