Problem #1: An investor with $10000 invests part of the money at 8% and the rest at 12%. How much should be invested at each rate to yield 11% of the total amount?

Problem #2: Suppose in 1960, the consumer price index was 70 while in 2015 it is 280. What monthly salary in 2015 would have the same purchasing power as a monthly salary of 800 dollars in 1960?

Rest if you want some more of them then you should take a look on Quora: Mitchell Lee's answer to What are some cool math problems? - Quora