# Are you sure the flight is safe?

Level pending

An airplane has 4 engines. The probability for the engines to function are $$\frac{1}{2}$$, $$\frac{2}{3}$$, $$\frac{3}{7}$$ and $$\frac{7}{8}$$ respectively. The airplane can fly if at least 1 of the engines can function. The probability that the airplane can fly safely can be expressed as $$\frac{a}{b}$$ where $$a$$ and $$b$$ are positive coprime integers. What is the value of $$a+b$$?

×