dNumber of photographs:_{1}= (multiple of 9) + 4 d_{2}= (multiple of 9) + 6

dThe photographer therefore exposed six frames on his last film._{1}x d_{2}= (multiple of 9) + (4 x 6) = (multiple of 9) + (18 + 6) = (multiple of 9) + 6

There are three frames left.

Source: Berrondom, Marie

Categories: Number sense, Modular arithmetic, Algebra, Reasoning

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