Question

What's the sum of all numbers less than 10,000 that are divisible by 2, 3, and 5??

Answer 1

It has a factor of 2*3*5=30
what is the biggest number that is  a multipule of 30

hmm
9000
9900
9990 is the biggest
30*333=9990
the summation of an arithetic sequence where first term is a1 and last is an and the number of terms is n
$s= \frac{n(a1+an)}{2}$

30 *2=60
that's 2 terms
30*3=90
30,60,90
3 terms

so 30*n means n terms
9990=30*333 means 333 terms

n=333
a1=30
an=9990
$s= \frac{333(30+9990)}{2}$
$s= \frac{333(10020)}{2}$
$s= \frac{3336660}{2}$
s=1668330

answer is 1,668,330