Question

sum of 70+71+72+73...100

Answer 1

the answer of this is 2564........

Answer 2

Its a A.P with '$a_{1}$' as 70 and 'd' as 1 and 'l(last term)' as 100

Using the formula :-

$a_{n} = a + (n-1)d$

We can find 'n' as

$100 = 70 + (n-1)*1$
[tex](n-1) = 100 - 70 [/tex]
$n = 30 -1 = 29$

Thus now we can use the formula, to find the sum...

$S_{n} = \frac{n}{2}( a_{1}+l )$
$S_{n} = \frac{29}{2}(70+l00 )$
Which simplifies to ...
$S_{n} = 2465$