1. find the sum of first 12 multiple of 12

Solution:
First 12 Multiples of 12

12	`xx`	1	=	12
12	`xx`	2	=	24
12	`xx`	3	=	36
12	`xx`	4	=	48
12	`xx`	5	=	60
12	`xx`	6	=	72
12	`xx`	7	=	84
12	`xx`	8	=	96
12	`xx`	9	=	108
12	`xx`	10	=	120
12	`xx`	11	=	132
12	`xx`	12	=	144

Multiples of 12 are `12,24,36,48,60,72,84,96,108,120,132,144`

Adding the multiples, the Sum is `936`

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2. find the sum of first 8 multiple of 3

Solution:
First 8 Multiples of 3

3	`xx`	1	=	3
3	`xx`	2	=	6
3	`xx`	3	=	9
3	`xx`	4	=	12
3	`xx`	5	=	15
3	`xx`	6	=	18
3	`xx`	7	=	21
3	`xx`	8	=	24

Multiples of 3 are `3,6,9,12,15,18,21,24`

Adding the multiples, the Sum is `108`

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3. find the sum of first 15 multiples of 8

Solution:
First 15 Multiples of 8

8	`xx`	1	=	8
8	`xx`	2	=	16
8	`xx`	3	=	24
8	`xx`	4	=	32
8	`xx`	5	=	40
8	`xx`	6	=	48
8	`xx`	7	=	56
8	`xx`	8	=	64
8	`xx`	9	=	72
8	`xx`	10	=	80
8	`xx`	11	=	88
8	`xx`	12	=	96
8	`xx`	13	=	104
8	`xx`	14	=	112
8	`xx`	15	=	120

Multiples of 8 are `8,16,24,32,40,48,56,64,72,80,88,96,104,112,120`

Adding the multiples, the Sum is `960`

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