If you can see 8 + 7 = 15 on one side of this ingenious flip book, then I will see 15 - 7 = 8 on the other! Guess inverse addition and subtraction number sentences in pairs, groups or with the whole class to add one digit numbers to 2-digit numbers to 20 and understand the inverse relationship between addition and subtraction. Consistent place value colour-coding is used throughout the number "flip-tabs". Flip book measures 260mm x 85mm and is suitable for ages 6-adult who will always need to keep practising this knowledge to keep it ready for rapid recall. Also great for working out missing numbers in addition & subtraction number sentences.