Question

Find the sum of two digit numbers that are completely divisible by 3

Answer 1

≡QUESTION≡

Find the sum of two digit numbers that are completely divisible by 3.

                                                           

║⊕ANSWER⊕║

The 2 digits no: include

12, 15, 18, ..... 99

a = 12

d = 3

aₙ = 99

n = ?

a + (n-1)d = aₙ

12 + (n-1)3 = 99

(n-1)3 = 99 - 12

n-1 = 87/3

n = 29+1

n = 30

Sₙ = n/2 (a + aₙ)

    =30/2 (12 + 99)

    = 15 (111)

    = 1665