XXX x XX (1 2-digits number and 1 3-digit number)

Formulas :

( __ x __ )[( __ x __ ) + ( __ x __ )][( __ x __ ) + ( __ x __ )]( __ x __ )

Example :

121 × 23

( 1 x 2 )[( 1 x 3 ) + ( 2 x 2 )][( 2 x 3 ) + ( 1 x 2 )]( 1 x 3 )

(2)(3 + 4)(6 + 2)(3)

(2)(7)(8)(3)

So, 121 × 23 = 2783