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Moderate

Probability of Selected Number

SATSTM-1EUVK5

If a is a number chosen from the set ${7, 9, 11, 13}$ and $b$ is chosen from the set ${2, 4, 8, 12, 16}$, then what is the probability that $a+b=21$?

A

$0.5$

B

$0.3$

C

$0.25$

D

$0.2$

E

$0.1$