**Solution :**

**i) 12,15 and 21**

12=2×2×3

15=5×3

21=7×3

From the above ,HCF(12,15,21)=3and LCM(12,15,21)=420

**ii)17,23,and 29**

17=17×1

23=23×1

29=29×1

From the above ,HCF(17,23,29)=1and LCM(17,23,29)=11339

**iii)8,9 and 25**

8=2×2×2

9=3×3

25=5×5

From the above ,HCF(8,9,25)=1and LCM(8,9,25)=1800