Question

Find the sum of all natural numbers between 20 and 224 which are divisible by 5.

Answer 1

Answer:

4900

Step-by-step explanation:

For starters, as the numbers are between 20 and 224, we will not take these two numbers.

I will use arithmetic progression to solve this problem.

a = 25, $a_n=220$ and d = 5

Now, to find n, we will use the formula: $a_n=a+(n-1)d$

220=25 + (n - 1) * 5

220 = 25 + 5n - 5

5n = 200, n = 40.

Now, using the formula $S_n=\frac{n}2[2a+(n-1)d]$

$S_n=\frac{40}2[2*25+39*5]$

$S_n=20[50+195]$$=20*245=4900$

Hence, the sum of all natural numbers between 20 and 224 which are divisible by 5 is 4900.

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