Children with Down Syndrome generally show a pattern of retarded mental development, although some achieve higher intellectual levels than others. The intellectual achievements of Down Syndrome children have been studied by numerous investigations, and several different types of chromosomal abnormalities associated with the syndrome have been identified. Two such abnormalities are called trisomy 21 and mosaicism. The levels of intellectual functioning of trisomy 21 and Mosaic Down Syndrome were compared in the paper Solution H0: mu1 = mu2 Ha: mu1 >mu2 Right tailed test at 0.05 The T-value is 3.546415. The P-Value is 0.00039. The result is significant at p < 0.05..