Question

the sum of all two digit order number is​

Answer 1

Answer:

ok

Step-by-step explanation:

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thnx for free points

Answer 2

Step-by-step explanation:

Sum of 'n' numbers is

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

first 2 digit number = 10, difference between any 2 successive numbers = 1, last number= 99, no.of digits from 10 to 99 = 90

Sn = 90/2 [2(10)+(90-1)1]

Sn = 45[20+89]

Sn = 45[109]

Sn = 4905

therefore, sum of all 2 digit numbers = 4905

2nd method:

Sn = n/2 [a+l]

first 2 digit number (a) = 10, last number(l) = 99, no.of digits from 10 to 99 = 90

Sn = 90/2 [10+99]

Sn = 45(109)

Sn = 4905