Question

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15​

Answer 1

Step-by-step explanation:

let a= 1

d=1

an= 15

n=15

s n=n/2(a+an)

= 15/2(1+15)

15 x 8

= 120

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Answer 2

Answer:

1+2=3

3+3=6

6+4=10

10+5=15

15+6=21

21+7=28

28+8=36

36+9=45

45+10=55

55+11=66

66+12=78

78+13=91

91+14=105

105+15=120