Relationships between Unknowns: Sum and Difference with Multiples

Methods in this video

Tap a time to jump to where the video teaches that method.

1. 1

   Two amounts: the smallest is 1 part

   ▶ 1:08

   When to use it: Two amounts are linked by a multiple (twice, 4 times as many, half), and the question gives their total or their difference.

   • The smaller amount is 1 part; the other is as many parts as the multiple.
   • Take away any known extra first; total ÷ total parts, or difference ÷ extra parts, gives 1 part.
   • Multiply by the parts the question asks for.
2. 2

   A chain: line up the shared amount

   ▶ 5:07

   When to use it: Three or more amounts are linked one after another (half of, so many times), or one amount is mentioned twice; the question asks for a total, one amount, or how many times one is another.

   • Start from the smallest amount: it is 1 part.
   • If one amount is mentioned twice, line its parts up first; if there is a half part, double everything.
   • To compare, just compare the parts; with a total, find 1 part first.