Adding, subtracting and multiplying fractions. Part of below zero and beyond.
Adding, subtracting and multiplying fractions · Alberta Grade 6 · maddyhelps.com
Find a common denominator first — the pieces have to be the same size before they can be added. Then multiply each fraction by the whole number. Simplify where you can.
A recipe needs 3/4 cup of flour. How much for 5 batches?
Different denominators
1/2 + 1/3 = 3/6 + 2/6 = 5/6; 2/3 + 1/4 = 8/12 + 3/12 = 11/12; 5/6 − 1/4 = 10/12 − 3/12 = 7/12; 3/4 − 2/3 = 9/12 − 8/12 = 1/12; 1/2 + 3/8 = 4/8 + 3/8 = 7/8; 7/10 − 1/5 = 7/10 − 2/10 = 5/10 = 1/2. 3 × 2/5 = 6/5 = 1 1/5; 4 × 3/8 = 12/8 = 1 1/2; 6 × 2/3 = 12/3 = 4. Flour: 5 × 3/4 = 15/4 = 3 3/4 cups.
Adding tops and bottoms — 1/2 + 1/3 = 2/5 — is the mistake. 2/5 is less than 1/2, one of the pieces being added, which shows it cannot be right.
Why this matters is on the below zero and beyond page. More sheets