Question 1029612
Call the number of 4-mark and 5-mark questions, x and y.
Then we can write
x + y = 18  and
4x + 5y = 83
Now multiply the top one by 4 and subtract and we get
4x + 5y = 83
-(4x + 4y = 72)
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y = 11
so that x = 7
Then the answer is 11 5-mark questions.