range

vipulgoyal wrote:the sum of the 10 numbers is 28, if the range of these numbers is 2, how many 3 are there

Let us assume the a is the smallest number and b is the largest number.
Hence, b = (a + 2)

Now let us consider the two extreme cases,

• When all the intermediate numbers are equal to the smallest
  sum = (9a + b) = (10a + 2) --> a = (28 - 2)/10 = 2.6 --> b = 4.6
  When all the intermediate numbers are equal to the largest
  sum = (a + 9b) = (10a + 18) --> a = (28 - 18)/10 = 1 --> b = 3

Hence, we can at least have the following two sets

• {2.6, 2.6, 2.6, 2.6, 2.6, 2.6, 2.6, 2.6, 2.6, 4.6} ---> No 3
  {1, 3, 3, 3, 3, 3, 3, 3, 3, 3} ---> Nine 3

Hence, we can only conclude that the minimum number of 3s in the set is 0 and the maximum number of 3s in the set is 9.

Note : In case someone is looking for some examples with 2 or 3 or etc number of 3 in the set, here you go...
{2.4, 2.6, 2.6, 2.6, 2.6, 2.6, 2.6, 2.6, 3, 4.4} ---> One 3
{1.7, 2.6, 2.6, 2.6, 2.6, 2.6, 2.6, 3, 3, 3.7} ---> Two 3s
{1.6, 2.6, 2.6, 2.6, 3, 3, 3, 3, 3, 3.6} ---> Five 3s
etc etc

sana.noor wrote:is this a gmat question?

Conceptually yes, but not in the format it has been posted.