When reducing fractions (finding an equivalent fraction) you have to determine a common divisor of both the numerator (top number) and the denominator (bottom number). For simplicity's sake 18 and 42 are both divisible by 2 so they can be reduced to 9 over 21.
When each factor is multiplied by 2 again the fraction is still equal to 18/42. However, in this instance you can see that 9 and 21 still have a common factor and can still be reduced. Consider the number 3 this time. After dividing again the most simplified equivalent factor is 3 over 7.
(The most simplified form of a fraction is often what most math professors look for)
42/50
2/3
The fraction 42/60 simplifies to 7/10.
0.42 is a fraction. It is a fraction in decimal form rather than in the form of a ratio. However, that does not stop it being a fraction. Its equivalent, in rational form, is 42/100. You can simplify this rational fraction if you require.
42/11 = 3.8181 . . .
18/42 = 3/7 in its simplest form
18/42 = 3/7
equivalent fraction for 21 over 23 = 42/46
18/42 = 3/7
7/8
42/50
2/3
7/9
2/5
1/2 ,
2/7
3/7