Question

find the sum of all natural numbers between 99 and 1001 which are multiple of 5 ​

Answer 1

Answer:

the given answer is based on ch 5 of class 10

Step-by-step explanation:

A/Q

the first no.(a)= 100

last no.(an) =1000

commom difference(d) = 5

then,

an =a+(n-1) d

1000 = 100+(n-1) 5

1000 = 100 +5n-5

1000 = 100 -5 +5n

1000 = 95 +5n

1000-95 = 5n

905 = 5n

n = 905/ 5

[ n = 181 ]

Sn = n/2 [2a+(n-1)d]

Sn = 181/2 [2×100 +(181-1) ×5]

Sn = 9.5 ×[ 200 + 180 ×5 ]

Sn = 9.5 (200+ 900)

Sn = 9.5 ×1100

Sn = 10450

Thus, the sum of no. between 99 and 1001 is 10450