4.NF.B.4.b: Understand a multiple of a/b as a multiple of 1/b and use this understanding to multiply a whole number by a fraction. For example, use a visual fraction model to express 3 × 2/5 as 6 × 1/5, recognizing this product as 6/5. (In general, n x a/b = (n x a)/b = (n x a) x 1/b.)