How do you multiply three digit numbers by two digit numbers?

Answer 1

Let x = abc be a 3-digit number. The expanded for of x is 100*a + 10*b + c.And let y = de = 10*d + e be a 2-digit number.

Then x*y =

1000*a*d + 100*a*e + 100*b*d + 10*b*e + 10*c*d + c*e

= 1000*a*d + 100*(a*e + b*d) + 10*(b*e + c*d) + c*e.