Cross-Multiplication Method (2×2)

Distribute the smaller factor across the place values of the larger number, then add the partial products.

1. 01

   2·5=10

   Run the partial calculation — running product 10.

2. 02

   2·8+3·5=31

   Now add the ones (3). Easy — it doesn't pass a new ten. 2 + 3 = 31 — running product 31.

3. 03

   3·8=24

   Run the partial calculation — running product 24.

4. →

   = 1334

Distribute the smaller factor across the place values of the larger number, then add the partial products.

1. 01

   4·8=32

   Run the partial calculation — running product 32.

2. 02

   4·6+7·8=80

   Now add the ones (7). Easy — it doesn't pass a new ten. 4 + 7 = 80 — running product 80.

3. 03

   7·6=42

   Run the partial calculation — running product 42.

4. →

   = 4042

Distribute the smaller factor across the place values of the larger number, then add the partial products.

1. 01

   Cross: (30)(40)=1200; outer+inner=(30×8)+(6×40)=480; 6×8=48

   Run the partial calculation — running product 48.

2. →

   = 1728

Benjamin, Secrets of Mental Math — cross-multiplication

Distribute the smaller factor across the place values of the larger number, then add the partial products.

1. 01

   Cross: (20)(70)=1400; outer+inner=(20×3)+(6×70)=480; 6×3=18

   Run the partial calculation — running product 18.

2. →

   = 1898

Benjamin, Secrets of Mental Math — cross-multiplication

Distribute the smaller factor across the place values of the larger number, then add the partial products.

1. 01

   Cross: (60)(70)=4200; outer+inner=(60×2)+(3×70)=330; 3×2=6

   Run the partial calculation — running product 6.

2. →

   = 4536

Benjamin, Secrets of Mental Math — cross-multiplication