a \(\dfrac{4}{7}\times\dfrac{21}{16}\times\dfrac{8}{5}=\dfrac{6}{5}\)

b \(\dfrac{34}{35}:x=\dfrac{17}{5}\)

\(x=\dfrac{34}{35}:\dfrac{17}{5}\)

\(x=\dfrac{34}{35}\times\dfrac{5}{17}\)

\(x=\dfrac{2}{7}\)

hears

D

\(\dfrac{15}{8}-\dfrac{4}{9}\times\dfrac{6}{8}+\dfrac{1}{6}=\dfrac{15}{8}-\dfrac{24}{72}+\dfrac{1}{6}=\dfrac{15}{8}-\dfrac{1}{3}+\dfrac{1}{6}=\dfrac{45}{24}-\dfrac{8}{24}+\dfrac{4}{24}=\dfrac{\left(45-8+4\right)}{24}=\dfrac{41}{24}\)

15/8−4/9×6/8+1/6=15/8−24/72+1/6=15/8−1/3+1/6

=45/24−8/24+4/24=(45−8+4)/24=41/24

A

REFER

a 

b 

Vì Đ₁ và Đ₂ mắc song song nên

I = I₁ + I₂ = 0,5 + 0,3 = 0,8 (A)

Vì Đ₁ và Đ₂ mắc song song nên

U = U₁ = 3V

A

\(\left(\dfrac{1}{4}+\dfrac{3}{4}\right)+\left(\dfrac{2}{5}+\dfrac{3}{5}\right)=\dfrac{4}{4}+\dfrac{5}{5}=1+1=2\)