The bond one is definitely the hardest, but still easy if you know what's going on. When you buy a bond, what you are really doing is buying a fixed amount of money in the future. If the interest rate is 4% and you buy a 1 year bond for $100, you should get $104 next year; if it's 6% then you should get $106 next year. Conversely, if the interest rate is 4% then $100 next year will cost you ~$96 now, and if it's 6% it'll cost you ~$94 now. (Actually, $96.15 and $94.34, because interest is multiplicative rather than additive).