Find the smallest positive integer n such that 5n+2n5n+1+2n+1>4.99.
A number or a short expression. Spacing and $ signs are ignored.
Solution
Writing 5n+1=5⋅5n and 2n+1=2⋅2n and cross-multiplying yields 0.01⋅5n>2.99⋅2n, and re-arranging yields (2.5)n>299. A straightforward calculation shows that the smallest n for which this is true is n=7.
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