Toss coin 1000 times got 550 heads, what is the probability the coin is unbiased?

From this item, we are given that 550 heads appeared out of the 1000 tosses of coins. We calculate for the number of tails by subtracting the number of head from the total number of tosses.
  tails = (1000 tosses) - (550 heads)
  tails = 450 

The probability in this item is calculated by dividing the number of heads from the total number of tosses.
   P = 550 / 1000 = 11/20

If the coin is not biased, the probability should have been 10/20 or 1/2 because there are only two sides of the coin and each is likely to occur. 

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The skating rink rented 872 pairs of skates during april and may.why? : if the skating rink rented three times the pair of skates in april during may, they rented 654 skates. 218 x 3 = 654then, if they want to know how many they rented during both april and may, then you just add 654 (may) and 218 (april) to give you 872 pairs of skates for both months.654 + 218 = 872hope this !