Everyday Mathematics

Trade-First Subtraction

Trade-First Subtraction As the name suggests, trade-first subtraction involves making all place-value trades first. This makes trade-first easier because we don’t have to switch back and forth between subtracting and trading.

Everyday Mathematics

Trade-First Subtraction Solve: 471 – 293 We set up the problem by writing the numbers in their place-value columns.

H = hundreds T = tens O = ones T O H 4 7 1 – 2 9 3

Everyday Mathematics

Trade-First Subtraction Solve: 471 – 293 First we must decide where trades need to be made. The trades can be made in any order.

Here we start with the ones place. Because 1 minus 3 results in a negative number, we trade 1 ten for 10 ones.

H T O 6 11 4 7 1 – 2 9 3

Everyday Mathematics

Trade-First Subtraction Solve: 471 – 293 Next we look at the tens place. Because 6 minus 9 results in a negative number, we trade 1 hundred for 10 tens.

H T O 3 16 11 4 7 1 – 2 9 3

Everyday Mathematics

Trade-First Subtraction Solve: 471 – 293 Now that all trades have been made, we can subtract in any place-value order.

471 – 293 = 178 H T O 3 16 11 4 7 1 – 2 9 3 1 7 8

Everyday Mathematics

Trade-First Subtraction When children use trade-first subtraction they practice a variety of skills related to number sense and algebraic reasoning. For example: • • • Writing numbers using place value; Breaking a hundred into 10 [10s] and breaking a ten into 10 [1s]; and Renaming numbers after shifting a group of 10 [10s] or 10 [1s] to the place-value column to the right.

Everyday Mathematics