Recognise and use the inverse relationship between addition and subtraction and use this to check calculations and solve missing number problems
| 1. | Odd or Even? Click the even numbers. | |
| 2. | Odd or Even? Click the odd numbers. | |
| 3. | Changing numbers: 36 to 39 | |
| 4. | Changing Numbers: 24 to 21 | |
| 5. | Changing Numbers: 66 to 76 | |
| 6. | Changing Numbers: 80 to 78 | |
| 7. | Changing Numbers: 50 to 45 | |
| 8. | Changing Numbers: 35 to 40 | |
| 9. | Changing Numbers: 48 to 47 | |
| 10. | Changing Numbers: 27 to 29 | |
| 11. | Changing Numbers: 68 to 58 | |
| 12. | Changing Numbers: 90 to 85 | |
| 13. | Changing Numbers: 66 to 76 | |
| 14. | Changing Numbers: 10 to 15 | |
| 15. | Changing Numbers: 20 to 30 | |
| 16. | Changing Numbers: 45 to 35 | |
| 17. | Changing Numbers: 90 to 100 | |
| 18. | Changing Numbers: 85 to 80 | |
| 19. | Changing Numbers: 45 to 50 | |
| 20. | Changing Numbers: 99 to 100 | |
| 21. | Changing Numbers: 24 to 14 | |
| 22. | Changing Numbers: 85 to 80 | |
| 23. | Changing Numbers: 48 to 50 | |
| 24. | Number Detectives ? + 3 = 6 | |
| 25. | Number Detectives: ? + 5 = 11 | |
| 26. | Number Detectives: 6 + ? = 9 | |
| 27. | Number Detectives: ?+5 = 15 | |
| 28. | Number Detectives: 9 + ? = 15 | |
| 29. | Number Detectives: 8 + ? = 15 | |
| 30. | 11 + 6 = 17: So what else is true? | |
| 31. | Changing Numbers: 24 to 34 | |
| 32. | Changing Numbers: 25 to 26 | |
| 33. | Changing Numbers: 17 to 21 | |
| 34. | Changing Numbers: 10 to 21 | |
| 35. | Changing Numbers: 7 to 11 | |
| 36. | Changing Numbers: 8 to 13 | |
| 37. | Changing Numbers: 9 to 12 | |
| 38. | Changing Numbers: 17 to 21 | |
| 39. | Changing Numbers: 18 to 21 | |
| 40. | Changing Numbers: 27 to 31 | |
| 41. | Changing Numbers: 24 to 28 | |
| 42. | Changing Numbers: 29 to 39 | |
| 43. | Changing Numbers: 30 to 50 | |
| 44. | Changing Numbers: 48 to 50 | |
| 45. | Number Detectives: ? + 10 = 32 | |
| 46. | Number Detectives: 10 + ? = 34 | |
| 47. | 11+6=17: So what else is true? | |
| 48. | 21+5=26: So what else is true? | |
| 49. | 15+12=27: So what else is true? | |
| 50. | True or False?: 21 + 4 = 25 | |
| 51. | True or False?: 23 + 2 = 27 | |
| 52. | True or False?: 26 + 3 = 29 | |
| 53. | True or False?: 24 + 4 = 25 | |
| 54. | True or False?: 22 + 6 = 28 | |
| 55. | Make 19: 8+6+? | |
| 56. | Make 18: 4+11+? | |
| 57. | Make 20: 9+11+? | |
| 58. | Make 20: 9+6+? | |
| 59. | Number detectives: Mysteries of 15 | |
| 60. | Number detectives: Mysteries of 16 | |
| 61. | Number detectives: Mysteries of 13 | |
| 62. | Number detectives: Mysteries of 17 | |
| 63. | Number detectives: Mysteries of 14 | |
| 64. | True or False?: 9 + 8 = 10 | |
| 65. | True or False?: 42 + 7 = 49 | |
| 66. | True or False?: 53 + 2 = 60 | |
| 67. | Make 30: 20 + 7 + ? = 30 | |
| 68. | N/D Mysteries of 20! 17+, 11+, 15+ | |
| 69. | N/D Mysteries of 20! 7+, 10+, 8+ | |
| 70. | N/D Mysteries of 20! 6+, 9+, 3+ | |
| 71. | N/D Mysteries of 20! 20+, 5+, 2+ | |
| 72. | Changing numbers: 24 changes to 33 | |
| 73. | Changing numbers: 19 changes to 28 | |
| 74. | Changing numbers: 13 changes to 21 | |
| 75. | Changing numbers: 9 changes to 17 | |
| 76. | Changing numbers: 8 changes to 17 | |
| 77. | Number Detectives: ? + 7 = 30 | |
| 78. | Number Detectives: ? + 24 = 30 | |
| 79. | True or False?: 17 + 4 = 20 | |
| 80. | True or False?: 9 + 8 = 16 | |
| 81. | True or False?: 5 + 6 = 12 | |
| 82. | True or False?: 16 + 3 = 18 | |
| 83. | True or False?: 9 + 7 = 17 | |
| 84. | Number Detectives: 22 + ? = 30 | |
| 85. | Number Detectives: 21 + ? = 30 | |
| 86. | Make 36: 20 + 14 + ? | |
| 87. | Make 39: 30 + 6 + ? | |
| 88. | Make 37: 12 + 20 + 5 | |
| 89. | Number detectives: 80+?, 90+?, 40+?=100 | |
| 90. | Number detectives: 10+?, 70+?, 50+?=100 | |
| 91. | Addition Chains: 3 + 2 + 4 + 8, 4 + 3 + 7 + 4 | |
| 92. | 100 Zone: 93 + 10, 94 + 10, 96 + 10 | |
| 93. | 100 Zone: 90 + 10, 92 + 10, 97 + 10 | |
| 94. | 100 Zone: 95 + 10,10 + 95, 105 - 10 | |
| 95. | 100 Zone: 98 + 10,10 + 98, 108 - 10 | |
| 96. | 100 Zone: 99 + 10,109 - 10, 10 + 99 | |
| 97. | True or False: 7+8=12 | |
| 98. | True or False: 17+2=20 | |
| 99. | True or False: 12+14=26 | |
| 100. | True or False: 12+12=24 | |
| 101. | True or False: 13+14=28 | |
| 102. | True or False: 15+12=27 | |
| 103. | True or False: 16+11=25 | |
| 104. | Number detectives: 35+? = 46 | |
| 105. | N/D Mysteries of 40! 34+? 30+? 38+?=40 | |
| 106. | N/D Mysteries of 40! 31+? 36+? 30+?=40 | |
| 107. | N/D Mysteries of 40! 33+? 37+? 32+?=40 | |
| 108. | N/D Mysteries of 40! 32+? 39+? 34+?=40 | |
| 109. | N/D Mysteries of 40! 31+? 35+? 37+?=40 | |
| 110. | Changing Numbers 14 to 54 | |
| 111. | Changing Numbers 35 to 85 | |
| 112. | Ball skills: How many more to make 10? 7+2+? | |
| 113. | Ball skills: How many more to make 10? 6+3+? | |
| 114. | Ball skills: How many more to make 10? 5+3+? | |
| 115. | Ball skills: How many more to make 10? 7+1+? | |
| 116. | Ball skills: How many more to make 10? 2+3+? | |
| 117. | Number detectives: ? - 5 = 10 | |
| 118. | Number detectives: ? - 6 = 3 | |
| 119. | Number detectives: ? - 7 = 2 | |
| 120. | Number detectives: ? - 7 = 6 | |
| 121. | Number detectives: ? - 8 = 4 | |
| 122. | Number detectives: 14 - ? = 4 | |
| 123. | Number detectives: 11 - ? = 5 | |
| 124. | Number detectives: 10 - ? = 8 | |
| 125. | Number detectives: 13 - ? = 5 | |
| 126. | Number detectives: 14 - ? = 7 | |
| 127. | Write the missing number: 15 + 1 + ? = 20 | |
| 128. | Write the missing number: ? + 11 + 2 = 20 | |
| 129. | Write the missing number: 3 + 4 + ? = 20 | |
| 130. | Write the missing number: ? + 5 + 6 = 20 | |
| 131. | Write the missing number: 5 + 8 + ? = 20 | |
| 132. | Number detectives ? -3 = 11 | |
| 133. | Number detectives 17 -? = 5 | |
| 134. | Changing numbers: 18 to 9 | |
| 135. | Changing numbers: 16 to 12 | |
| 136. | Changing numbers: 12 to 7 | |
| 137. | Changing numbers: 20 to 9 | |
| 138. | Changing numbers: 14 to 9 | |
| 139. | Write the missing number: 4 + 8 + ? = 20 | |
| 140. | Write the missing number: ? + 13 + 4 = 20 | |
| 141. | Write the missing number: 4 + ? + 6 = 20 | |
| 142. | True or False? 18-9=0 | |
| 143. | Take 10: ? - 10 = 60 | |
| 144. | Write the missing number: 8 + ? + 7 = 20 | |
| 145. | Write the missing number: 6 + ? + 8 = 20 | |
| 146. | Write the missing number: ? + 9 + 6 = 20 | |
| 147. | Write the missing number: 2 + 11 = ? = 20 | |
| 148. | Write the missing number: ? + 7 + 9 = 20 | |
| 149. | Subtraction chain 20 - 5 = 15, 15 - 2 = ? | |
| 150. | Subtraction chain 20 - 12 = ? - 6 = 2 | |
| 151. | Hide and seek: 10 trolls - 5 | |
| 152. | Hide and seek: 14 trolls - 5 | |
| 153. | Hide and seek: 11 trolls - 5 | |
| 154. | Put in the missing number: 9 + 2 + ? = 19 | |
| 155. | Put in the missing number: ? + 10 + 14 = 28 | |
| 156. | True or False?: 29 - 7 = 23 | |
| 157. | True or False?: 28 - 5 = 21 | |
| 158. | True or False?: 24 - 2 = 20 | |
| 159. | True or False?: 15 - 3 = 10 | |
| 160. | True or False?: 8 - 5 = 2 | |
| 161. | True or False?: 27 - 4 = 23 | |
| 162. | True or False?: 25 - 5 = 20 | |
| 163. | Subtraction Chain - 22-4=?-3=15 | |
| 164. | Subtraction Chain - ?-8=16-2=14 | |
| 165. | Subtraction Chain - 21-4 =?-1= 16 | |
| 166. | Subtraction Chain - ?-4=21-2=19 | |
| 167. | Subtraction Chain - 27-4=?-6=17 | |
| 168. | Subtraction Chain - ?-4=19-3=16 | |
| 169. | Mysteries of Fifty: 50-?=42, 50-?=45 | |
| 170. | Mysteries of Fifty: 50-?=48, 50-?=43 | |
| 171. | Mysteries of Fifty: 50-?=44, 50-?=47 | |
| 172. | Mysteries of Forty: 40-?=36, 40-?=31 | |
| 173. | Mysteries of Forty: 40-?=33, 40-?=39 | |
| 174. | Mysteries of Forty: 40-?=35, 40-?=38 | |
| 175. | Mysteries of Thirty: 30-?=29, 30-?=24 | |
| 176. | Mysteries of Thirty: 30-?=21, 30-?=27 | |
| 177. | Mysteries of Thirty: 30-?=26, 30-?=22 | |
| 178. | True or False?: 23 - 5 = 18 | |
| 179. | True or False?: 21 - 16 = 4 | |
| 180. | True or False?: 18 - 9 = 8 | |
| 181. | True or False?: 19 - 6 = 12 | |
| 182. | True or False?: 24 - 15 = 8 | |
| 183. | True or False?: 22 - 10 = 11 | |
| 184. | True or False?: 19 - 13 = 6 | |
| 185. | True or False?: 26 - 13 = 13 | |
| 186. | Spot the difference between 30 and 15. | |
| 187. | Spot the difference between 12 and 25. | |
| 188. | Spot the difference between 30 and 10. | |
| 189. | Spot the difference between 40 and 10. | |
| 190. | Spot the difference between 20 and 39. | |
| 191. | Spot the difference between 18 and 25. | |
| 192. | Spot the difference between 25 and 34. | |
| 193. | Spot the difference between 19 and 31. | |
| 194. | Spot the difference between 19 and 42. | |
| 195. | Spot the difference between 36 and 15. | |
| 196. | Number detectives: ? + 23 = 30 | |
| 197. | Number detectives: ? + 18 = 30 | |
| 198. | True or False?: 30 - 8 = 22 | |
| 199. | True or False?: 30 - 25 = 20 | |
| 200. | True or False?: 30 - 10 = 20 | |
| 201. | True or False?: 30 - 10 = 15 | |
| 202. | True or False?: 30 - 7 = 23 | |
| 203. | Number detectives: 30 - ? = 15 | |
| 204. | Number detectives: 30 - ? = 13 | |
| 205. | Spot the difference: 60 & 40, 12 & 18, 100 & 95 | |
| 206. | Spot the difference: 20 & 14, 17 & 9, 80 & 73 | |
| 207. | Spot the difference: 100 & 30, 19 & 11, 30 & 24 | |
| 208. | Spot the difference: 50 & 41, 100 & 92, 101 & 98 | |
| 209. | Subtracting tens: 44 - ? = 24 | |
| 210. | What Was I Thinking? - find original number after operations | |
| 211. | What Was I Thinking? - find original number after operations | |
| 212. | Which Operation? - 60*4 = 56 | |
| 213. | Number Quest - complete number sentence | |
| 214. | Number Quest - find 1 number to complete 2 number sentences | |
| 215. | Number Quest - find 1 number to complete 2 number sentences | |
| 216. | 16 go to WaterWorld: 5+4+3+? | |
| 217. | 17 go to Waterworld: 6+5+2+? | |
| 218. | 14 go to Waterworld: 6+3+2+? | |
| 219. | 18 go to WaterWorld: 3+3+2+? | |
| 220. | 15 go to WaterWorld: 5+3+2+? | |
| 221. | 16 go to Waterworld? 2+3+3+? | |
| 222. | 19 go to Waterworld: 5+4+3+? |