In a 3 x 4 dot rectangle there are 10 dots on the outside and 2 dots on the inside.In a 4 x 5 dot rectangle there are 14 dots on the outside and 6 dots on the inside.How may dots are outside in a 1989 x 1990 dot rectangle?

Answer 1

2x3 rectangle, the inside is 1x2
****
*oo*
****

4x5 rectangle, the inside is 2x3
*****
*ooo*
*ooo*
*****

3x6 rectangle, the inside is 1x4
******
*oooo*
******

Have you discovered the formula to calculate a 1989 x 1990 dot rectangle?

Answer 2

1987*1988=3,950,516

Answer 3

3950516