Let Ti, i=1, … ,n be a set of dates, on which payments of the floating leg of an interest
rate swap occur. The payoff of the floating leg of the swap at time Ti is Fi + s where Fi is
the reference rate of the floating leg and s is a constant spread. For simplicity, let’s
assume that the floating and fixed payments happen on the same dates. Also, ri is the
risk-free rate on the same tenor. Let N be the notional of the swap.
1) What is the fixed semiannual swap rate calculated from the risk-free rates? Please
specify mathematical formula (no need for exact numerical result at this point).
2) Let the semiannual swap rate calculated in 1) be the fixed leg payment of the
swap. What is the constant spread s which sets the present value of the swap
position to be zero? Please specify mathematical formula (no need for exact
numerical result at this point).

第一题是什么意思哇，计算半年期互换利率不是以对应的浮动利率为基础吗，这里的浮动利率是什么，什么叫calculated from risk-free rates???