After all 20 tosses of the coin, a tail was recorded 11 times. We can write this as 11/20.
To convert this into a decimal, we simply multiply the numerator and denominator by 5 so that the fraction is out of 100, giving us 55/100.
When we do the sum of 55 ÷ 100, we get the answer of 0.55.
I hope this helps!
