John had the average score of 84 on his first three Checkpoints. The first score was 67. The second score was 7 less than the third score. What are his scores in the second and third Checkpoints?

Question

John had the average score of 84 on his first three Checkpoints.  The first score was 67. The second score was 7 less than the third score.  What are his scores in the second and third Checkpoints?

anonymous · Answer

$$ Let\ s_2\ and\ s_3$$
be the scores on the second and third checkpoints respectively.
The average score would be 
$$ Average = \frac{s_1+s_2 + s_3}{3}$$
Since the score on the first checkpoint is 67, and the average is 84 we have:
$$84 = \frac{67 + s_2 +s_3}{3} $$
We are also given that the second score was 7 less than the third..
$$ \rightarrow s_2 = s_3-7$$

We have 2 equations and 2 unknowns. Solve for s2 and s3.