Fraction = part / whole. Always simplify to the lowest terms.

Find the number of pupils who passed: Total - Failed.
Pupils who passed	=	35 - 5 = 30
Fraction passed = (number passed) / (total number).
Fraction passed	=	\(\dfrac{30}{35}\)
Simplify: divide numerator and denominator by GCD(30, 35) = 5.
Simplified	=	\(\dfrac{30 \div 5}{35 \div 5} = \dfrac{6}{7}\)