Returns the probability associated with a Student's tTest. Use T.TEST to determine whether two samples are likely to have come from the same two underlying populations that have the same mean.
Syntax
T.TEST(array1,array2,tails,type)
The T.TEST function syntax has the following arguments:

Array1 Required. The first data set.

Array2 Required. The second data set.

Tails Required. Specifies the number of distribution tails. If tails = 1, T.TEST uses the onetailed distribution. If tails = 2, T.TEST uses the twotailed distribution.

Type Required. The kind of tTest to perform.
Parameters
If type equals 
This test is performed 
1 
Paired 
2 
Twosample equal variance (homoscedastic) 
3 
Twosample unequal variance (heteroscedastic) 
Remarks

If array1 and array2 have a different number of data points, and type = 1 (paired), T.TEST returns the #N/A error value.

The tails and type arguments are truncated to integers.

If tails or type is nonnumeric, T.TEST returns the #VALUE! error value.

If tails is any value other than 1 or 2, T.TEST returns the #NUM! error value.

T.TEST uses the data in array1 and array2 to compute a nonnegative tstatistic. If tails=1, T.TEST returns the probability of a higher value of the tstatistic under the assumption that array1 and array2 are samples from populations with the same mean. The value returned by T.TEST when tails=2 is double that returned when tails=1 and corresponds to the probability of a higher absolute value of the tstatistic under the “same population means” assumption.
Example
Copy the example data in the following table, and paste it in cell A1 of a new Excel worksheet. For formulas to show results, select them, press F2, and then press Enter. If you need to, you can adjust the column widths to see all the data.
Data 1 
Data 2 

3 
6 

4 
19 

5 
3 

8 
2 

9 
14 

1 
4 

2 
5 

4 
17 

5 
1 

Formula 
Description 
Result 
=T.TEST(A2:A10,B2:B10,2,1) 
Probability associated with a Student's paired tTest, with a twotailed distribution. 
0.196016 