Quartiles and Inter-Quartile Range

Why am I getting a wrong result for quartiles?

here is my code:

cbiomass = c(910, 1058, 929, 1103, 1056, 1022, 1255, 1121, 1111, 1192,
1074, 1415)

summary(cbiomass)

IQR(cbiomass)

The result R gives me is:

For the summary

Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 

910    1048    1088    1104    1139    1415 

For IQR

91.25

*********

The true Q1 is 1039 and not 1048. Q2 is 1156.5 and not 1139. And the
Inter-Quartile Range is 117.5 and not 91.25

How can I get these number right?

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