Question

find sum of term 1+3+5+........+79​

Answer 1

it is an AP where,

• a=1
• d=2
• l=79

using formula

$l = a + (n - 1)d$

$79 = 1 + (n - 1) \times 2$

$78 = (n - 1) \times 2$

$39 = n - 1$

$n = 40$

using formula for sum

$sn = \frac{n}{2} (a + l)$

$sn = \frac{40}{2} (1 + 79)$

$sn = 20 \times 80$

$sn = 1600$

HOPE IT HELPS

Answer 2

Answer:

1600 is the answer.

Step-by-step explanation:

A.P=1+3+5+.......+79

a=1

d=2

an=79

a+(n-1)d=an

1+(n-1)2=79

(n-1)2=78

(n-1)=78/2

=39

Thus n=40

NOW, Sn=n/2(a+an)

=40/2(1+79)

=40/2(80)

=40X40

=1600

Therefore the sum of terms 1+3+5+.....+79 is 1600.

HOPE IT HELPS.

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