Advance A

W3·D1

2-digit × 1-digit Multiplication

Decompose and add left-to-right.

Learning Objectives

  • 01

    Multiply any 2×1 in under 3 seconds.

Topics

Place-value decomposition

Worked Examples

53 × 6=318

Left-to-right multiplication (Benjamin): break the 2-digit number into tens + units, multiply each, add.

  1. 01

    50 × 6 = 300

    Tens first — biggest piece always goes first to keep the running total anchored.

  2. 02

    3 × 6 = 18

    Now the units piece.

  3. 03

    300 + 18 = 318

    Add the two partial products — left-to-right addition.

  4. →

    = 318

79 × 9=711

×9 shortcut (Benjamin): use (n × 10) − n.

  1. 01

    79 × 10 = 790

    Multiplying by 10 just shifts a zero on the end.

  2. 02

    790 − 79 = 711

    Subtract one copy of 79, because 9 = 10 − 1.

  3. →

    = 711

25 × 6=150

Left-to-right multiplication (Benjamin): break the 2-digit number into tens + units, multiply each, add.

  1. 01

    20 × 6 = 120

    Tens first — biggest piece always goes first to keep the running total anchored.

  2. 02

    5 × 6 = 30

    Now the units piece.

  3. 03

    120 + 30 = 150

    Add the two partial products — left-to-right addition.

  4. →

    = 150

Benjamin, Secrets of Mental Math — distribute by place

58 × 4=232

Left-to-right multiplication (Benjamin): break the 2-digit number into tens + units, multiply each, add.

  1. 01

    50 × 4 = 200

    Tens first — biggest piece always goes first to keep the running total anchored.

  2. 02

    8 × 4 = 32

    Now the units piece.

  3. 03

    200 + 32 = 232

    Add the two partial products — left-to-right addition.

  4. →

    = 232

Benjamin, Secrets of Mental Math — distribute by place

82 × 6=492

Left-to-right multiplication (Benjamin): break the 2-digit number into tens + units, multiply each, add.

  1. 01

    80 × 6 = 480

    Tens first — biggest piece always goes first to keep the running total anchored.

  2. 02

    2 × 6 = 12

    Now the units piece.

  3. 03

    480 + 12 = 492

    Add the two partial products — left-to-right addition.

  4. →

    = 492

Benjamin, Secrets of Mental Math — distribute by place

Talking Points

  • •Say the partial product aloud before adding the next.

Week 3 · Multiplication Essentials

2×1, 3×1, and factoring methods.

  • →Master 2×1 and 3×1
  • →Use addition vs subtraction methods
  • →Factor for speed

Sample Problems · Week 3

One simple and one intermediate problem to preview the week.

Simple · Day 1

53 × 6=318

Intermediate · Day 5

858 × 6=5148