The chance of getting heads is 1/2 because there are two sides of a coin. The chance of spinning a 4 is 1/10 because the 4 is only on space out of the ten on the wheel. Multiply these fractions to get the probability:
1/2 x 1/10 = 1/20. 1/20 is the answer for number 15.
16. 5/10 x 1/2 = 1/4
17. 3/10 x 1/2 = 3/20
18. 5/10 x 1/2 = 1/4