What is the average (arithmetic mean) of all multiples of 10

Hi tuanquang269,

This question can be solved with the Average Formula and 'bunching.'

We're asked for the average of all of the multiples of 10 from 10 to 400, inclusive.

To start, we can figure out the total number of terms rather easily:
1(10) = 10
2(10) = 20
...
40(10) = 400

So we know that there are 40 total numbers.

We can now figure out the SUM of those numbers with 'bunching':

10 + 400 = 410
20 + 390 = 410
30 + 380 = 410
Etc.

Since there are 40 total terms, this pattern will create 20 'pairs' of 410.

Thus, since the average = (Sum of terms)/(Number of terms), we have...

(20)(410)/(40) =
410/2 =
205

Final Answer:

GMAT assassins aren't born, they're made,
Rich