Question

Find the sum of all two digit odd multiples of 3.
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Answer 1

Heya user...!!

Here is ur answer...!!

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• The two digit odd multiples of 3. numbers  are :

                     15, 21, 27, 33, 39........99

Now , Here first term ( a ) = 15

Common difference(d) =  21 - 15 =   6

an ( last digits ) = 99

After, that we are going to apply an formula for finding n  :

• an = a + ( n - 1) d

• 99  = 15 + ( n - 1 ) 6

• 99 - 15 =  6n - 6

• 84 = 6n - 6

• 84 + 6 = 6n

• 90 = 6n

• n = 90/6

∴ n = 15

Now , we have to Find the sum of all two digit odd multiples of 3 :

We are going to find this by using Sn formula :

• Sn = n/2 ( 2a +( n-1) d )

• Sn=n/2(2a+(n-1)d)

• Sn=15/2(30+14(6)

• Sn = 15/2 (30+84)

• Sn = 15/2 × 114

• Sn = 15 × 57

• Sn = 855

∴ Sn = 855

Therefore, The sum of two digit odd multiples of 3 = 855

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I Hope this may help u...!!

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Answer 2

Answer:

855

Step-by-step explanation:

a = 15

d = 21-15 = 6

l = 99

an=a+(n-1)d

99=15+6n-6

99 = 9+6n

99-9 = 6n

90 = 6n

n =15

now sum of n terms=

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

s15=15/2(30+14(6))

s15 = 15/2(30+84)

s15 = 15/2*114

s15 = 15*57

s15 = 855

so the sum of all two digit odd multiples of 3 is 855