Find the missing probability in the table below.
x 1 2 3 4
p(x) 0.40 0.20 0.15 ?

X          1           2        3         4
p(x)    0.40    0.20   0.15     ?

If the items are only 4. The total of the probability must be 1 or 100%

1 - 0.40 - 0.20 - 0.15 = 0.25

The probability of 4 is 0.25.

When rates are expressed as a quantity of 1, such as 2 feet per second or 5 miles per hour, they are called unit rates. if you have a multiple-unit rate such as 120 students for every 3 buses, and want to find the single-unit rate, write a ratio equal to the multiple-unit rate with 1 as the second term.