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In an exam, two reasoning problems, 1 and 2, are asked. 35% students solved problem 1
and 15% students solved both the problems. How many students who solved the first
problem will also solve the second one?
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Before formulating my answer, I want to highlight/underline that NOBODY in the entire world CAN ANSWER the question correctly
(if to understand the question literally), because the total number of students is unknown.
So, in this sense, the question was formulated INCORRECTLY / inaccurately.
The correct / accurate formulation of the question is THIS:
Which fraction (or percentage) of those, who solved the first problem, solved the second problem too ?
And then the answer becomes OBVIOUS (or even more than obvious):
the fraction is , or .
the percentage is = 42.86%.