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+? |