1) 285 + 470 + 115 + 230
= (285 + 115) + (470 + 230)
= 400 + 700 = 1100

3) 46 + 17 + 54 - 17
= (46 + 54) + (17 - 17)
= 100

5) 2021 + 2023 + 979 - 23
= (2021 + 979) + (2023 - 23)
= 3000 + 2000 = 5000

7) 542 + 125 + 58 - 25
= (542 + 58) + (125 - 25)
= 600 + 100 = 700

9) 151 + 234 - 51 + 166
= (151 - 51) + (234 + 166)
= 100 + 400 = 500

11) 5 . 3 . 4 . 2 . 25
= 3 . (4 . 25)(2 . 5)
= 3 . 100 . 10 = 3000

13) 2 . 67 + 2 . 32 + 2
= 2 . (67 + 32 + 1)
= 2 . 100 = 200

15) 4 . 7 + 4 . 13
= 4 . (13 + 7) 
= 4 . 20 = 80

17) 997 + 129 + 3 - 29
= (997 + 3) + (129 - 29)
= 1000 + 100 = 1100

19) 714 + 382 + 286 + 318
= (714 + 286) + (382 + 318)
= 1000 + 700 = 1700

21) 48 . 17 + 48 . 2 + 48
= 48 . (17 + 2 + 1)
= 48 . 20 = 960

23) 91 . 157 - 29 . 91 - 91 . 28
= 91 . (157 - 29 - 28)
= 91 . 100 = 9100