A sample of 100 men has average height 70 in. and standard deviation 2.5 in. A sample

Question:

A sample of 100 men has average height 70 in. and standard deviation 2.5 in. A sample of 100 women has average height 64 in. and standard deviation 2.5 in. If both samples are combined, the standard deviation of all 200 heights will be
i. Less than 2.5 in.
ii. Greater than 2.5 in.
iii. Equal to 2.5 in.
iv. Can't tell from the information given.