A student scores $85\%$ in an examination. The scores were $79$, $81$, $88$ and $94$ in $4$ subjects. Find the student's score in the $5\text{th}$ subject.

1. Let the maximum marks for each subject be $100$. Since the student scores an overall average of $85\%$, the average marks per subject across $5$ subjects is $85$.
$$\text{Total marks in 5 subjects}=5\times 85=425$$

2. Sum the scores of the given $4$ subjects:

$$\text{Sum of 4 subjects}=79+81+88+94=342$$

3. Calculate the score of the $5\text{th}$ subject:

$$\text{Score in 5th subject}=425-342=83$$