3-digit × 1-digit Multiplication

Left-to-right 3×1 (Benjamin): hundreds, tens, units — each piece, then add.

1. 01

   300 × 7 = 2100

   Hundreds first.

2. 02

   20 × 7 = 140

   Tens next.

3. 03

   4 × 7 = 28

   Then units.

4. 04

   2100 + 140 + 28 = 2268

   Add as you go, left-to-right — say each running total aloud.

5. →

   = 2268

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

1. 01

   572 × 10 = 5720

   Multiplying by 10 just shifts a zero on the end.

2. 02

   5720 − 572 = 5148

   Subtract one copy of 572, because 9 = 10 − 1.

3. →

   = 5148

Left-to-right 3×1 (Benjamin): hundreds, tens, units — each piece, then add.

1. 01

   800 × 3 = 2400

   Hundreds first.

2. 02

   60 × 3 = 180

   Tens next.

3. 03

   3 × 3 = 9

   Then units.

4. 04

   2400 + 180 + 9 = 2589

   Add as you go, left-to-right — say each running total aloud.

5. →

   = 2589

Benjamin, Secrets of Mental Math — distribute left-to-right

Left-to-right 3×1 (Benjamin): hundreds, tens, units — each piece, then add.

1. 01

   300 × 7 = 2100

   Hundreds first.

2. 02

   80 × 7 = 560

   Tens next.

3. 03

   0 × 7 = 0

   Then units.

4. 04

   2100 + 560 + 0 = 2660

   Add as you go, left-to-right — say each running total aloud.

5. →

   = 2660

Benjamin, Secrets of Mental Math — distribute left-to-right

Left-to-right 3×1 (Benjamin): hundreds, tens, units — each piece, then add.

1. 01

   200 × 7 = 1400

   Hundreds first.

2. 02

   50 × 7 = 350

   Tens next.

3. 03

   5 × 7 = 35

   Then units.

4. 04

   1400 + 350 + 35 = 1785

   Add as you go, left-to-right — say each running total aloud.

5. →

   = 1785

Benjamin, Secrets of Mental Math — distribute left-to-right