Straight across. Numerators by numerators, and denominators by denominators.
What are the two ways you can multiply fractions by whole numbers?
1. The numerator of the product will be the whole number times the fraction's numerator, and the denominator will be the fractions denominator.
2. Treat the whole number as a fraction, the whole number over one, then multiply as you would any two fractions.
How do you divide with fractions?
Invert the second fraction and multiply straight across.
What are the two ways to reduce a fraction?
1. Use prime factorization on the numerator and the denominator. Make a fraction out of the primes you get from the numerator and the denominator by putting the numerators on top and the denominators on the bottom. Let common numbers from both sides cancel each other out. Let the remainders create a new, reduced fraction.
2. Find the largest number that divides both the numerator and the denominator. This number is called the greatest common divisor (GCD). Factor the GCD from the numerator and denominator and rewrite the fraction. Sometimes the greatest common divisor is not obvious. In these cases you might find it easier to reduce the fraction in several steps.