Question

find the sum of the first 40 positive integers divisible by 6. find the sum of the first 15 multiples of 8. find the sum of the odd number between 0 and 50​

Answer 1

Answer:

Positive integers divisible by 6 are

6,12,18,24,....

since difference is same, it is an AP

We need to find sum of first 40 integers

we can use formula

 Sn = $\frac{n}{2}$(2a + (n-1) d)

here n=40,

        a=6,

        d=12 - 6 = 6

putting values in formula

Sn = $\frac{40}{2}$(2 x 6 + (40-1) 6)

    = 20 (12 + 39 x 6 )

    = 20 (12 +234)

    =20 (246)

    Sn=4920

 

Answer 2

Answer:

4952, 960, 625

Explanation:

first 40 positive integers divisible by 6:

6 + 12 + 18 + 24 + 30 + 36 + 42 + 48 + 54 + 60 + 66 + 72 + 78 + 84 + 90 + 96 + 102 + 108 + 114 + 120 + 126 + 132 + 138 + 144 + 152 + 158 + 164 + 170 + 176 + 182 + 188 + 194 + 200 + 206 + 212 + 218 + 224 + 230 + 236 + 242 = 4952

first 15 multiples of 8:

8 + 16 + 24 + 32 + 40 + 48 + 56 + 64 + 72 + 80 + 88 + 96 + 104 + 112 + 120 = 960

odd numbers between 0 and 50:

1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19 + 21 + 23 + 25 + 27 + 29 + 31 + 33 + 35 + 37 + 39 + 41 + 43 + 45 + 47 + 49 = 625