Screens:

• First screen is login
• Force a login for access to the application, but create a guest account for people to use untracked (maybe "guest" or simply the empty string "" if that's possible)

For rounding:

• "Magic Numbers" for two digits: 10, 15, 25, 50, 75
• Allow teachers to set constraints (both on how it rounds and on how tight the answer must be)
• Examples given:

4444 + 555 --> 4000 + 600, 4400 + 600, 4400 + 500, 4500 + 500

4265 - 840 --> 4000-800, 4300-800, 4200-900

111 * 231 --> 100 * 200, 100 * 230

855 / 61 --> 900/60

68 + 14 --> 70 + 10, 70 + 15

605 + 403 --> 600 + 400

1,917 + 3,064 --> 2,000 + 3,000

4,987 + 5,062 --> 5,000 + 5,000

92 + 17 --> 90 + 20

256 + 55 --> 250 + 50, 260 + 60

147 + 198 --> 150 + 200 (again, 150 is easy to add to 200)

23 + 188 --> 25 + 200, but I would also accept 20 + 200

107 + 81 --> 110 + 80, 100 + 80, and 100 + 100

770+237 --> 800 + 200

638 +154 --> 600 + 200, 600 + 150

56 + 38 --> 60 + 40

723 + 129 --> 725 + 125, 750 + 100

359-216 --> 360-200, 400-200

490-137 --> 500-100, 500-150

37-18 --> 40-20

446-29 --> 450-30

565-29 --> 570-30

671-396 --> 700-400

96-7 --> 100-10

661-23 --> 660-20, 700-25

749-32 --> 750-30

45 * 81 --> 50 * 80

321 * 56 --> 300 * 60

47 * 23 --> 50 * 20

247 * 8 --> 250 * 8

49 * 9 --> 50 * 10

267 * 81 --> 300 * 80, 250 * 80

14 * 6 --> 15 * 5, 10 * 6

106 * 6 --> 100 * 6

48 * 5 --> 50 * 5