Endless possibilities in exploring addition, subtraction, counting on and general counting up to 20. How may windows do you see? Subtract the number of houses without chimneys from the total with. How many houses have 4 windows. All are compatible with dry wipe markers and Soluble OHP Pens. Size H-250mm W-250mm ALSO AVAILABLE: other designs and clear OHPs. Sold in various sized packs and individually.