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| 1. |
sum of all 2-digit multiples of 3 |
| Answer» Sum of 2digit multiples of 3 are:12,15,18,21..........................99a=12d=15-12 =3an=99an=a+(n-1)d99=12+(n-1)399-12 =3n-387=3n-33n=87+33n=90N=30Sn=n÷2(a+an)Sn=30÷2(12+99)Sn=15(111)Sn=1665 | |