There are three £1 coins and nine 50p coins. She takes 3 coins from the bag at random.

work out the probability that she takes exactly £2.50

so i know the answer is 27/220 but i do not know how you guys got to 220 can someone give me the calculation. not just "12c3= 220" cause i dont get it

answer: need picture of problem

step-by-step explanation:

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step-by-step explanation:

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answer: cos [   arcsin (3/5) - arccos (1/2) ] =

step-by-step explanation: × = 3/5 = 0.6--> x = 36.87 and x = 180 - 36.87 = 143.13 deg

cos y = 1/2 --> y = +- 60 deg a. cos (x - y) = cos (143.13 - 60) = cos 83,13  

=

0.12

b. cos (36.87 - 60) = cos (-23.23) = 0.92