$1 \times 2$:

$3 \times 5 = 15$

$2 \times 2$:

$4 \times 10 = 20$

$1 \times 3$:

$7 \times 10 = 70$

and a variation on that theme which works for $2 \times 3$:

$13 \times 10 = 130$

This is about as hard as I can solve without using even pen and paper to think them out (obviously I'm using Excel to make the pictures). FWIW I'm working on an iPad app to help with tiling by hand, it's a good exercise to polish my Swift.

$1 \times 2$:

$3 \times 5 = 15$

$2 \times 2$:

$4 \times 10 = 20$

$1 \times 3$:

$7 \times 10 = 70$

and a variation on that theme which works for $2 \times 3$:

$13 \times 10 = 130$

This is about as hard as I can solve without using even pen and paper to think them out (obviously I'm using Excel to make the pictures). FWIW I'm working on an iPad app to help with tiling by hand, it's a good exercise to polish my Swift. the app works now (more or less), and helped me finding a solution for $1 \times 4$:

$9 \times 10 = 90$

$1 \times 2$:

$3 \times 5 = 15$

$2 \times 2$:

$4 \times 10 = 20$

$1 \times 2$:

$3 \times 5 = 15$

$2 \times 2$:

$4 \times 10 = 20$

$1 \times 3$:

$7 \times 10 = 70$

and a variation on that theme which works for $2 \times 3$:

$13 \times 10 = 130$

This is about as hard as I can solve without using even pen and paper to think them out (obviously I'm using Excel to make the pictures). FWIW I'm working on an iPad app to help with tiling by hand, it's a good exercise to polish my Swift.