The means of two samples of size 40 and 50 were found to be 54 and 63 respectively. Their standard deviations were 6 and 9 respectively. The variance of the combined sample of size 90 is

The mean of two samples of sizes 200 and 300 were found to be 25, 10 respectively. Their standard deviations were 3 and 4 respectively. The variance of combined sample of size 500 is

The mean of two samples of sizes 200 and 300 were found to be 25,10 respectively.Their standard deviations were 3 and 4 respectively.The variance of combined sample of size 500 is

The means of two samples of sizes 500 and 600 were respectively 186 and 175. The corresponding standard deviations were respectively 9 and 10. The variable studied was height in centimetres. Obtain the mean and variance of the combined sample.

The means of two samples of sizes 10 and 20 respectively are 24 and 45 and the standard deviations are 6 and 11. Obtain the standard deviation of the sample of size 30 obtained by combining the two samples. (sqrt19067=138)