Question

A list of transactions contains 100 numbers: 60 gains and 40 losses. The gains are positive numbers and the the losses are negative numbers. The units are thousands of dollars. For the 60 gains, the average is 18 and the SD is 7.5. For the losses the average is -20 and the SD is 9.2.
a) Find the average of the 100 transactions  (answ: avg=2.8)
b) Find the SD of the 100 transactions.  (answ: SD=20.35)
 
how do i do this? (Answers given but please show work!). Thank you

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