Answer:
assume Par Value = 1000
Price = 1000
Coupon = 7%
Coupon = Coupon rate * Par Value/2 = 7% * 1000/2 = 35
For Sam Maturity = 6 years
Price = summation Coupont/(1+YTM/2)2t + Par Value/(1+YTM/2)2t
1000 = 35/(1+YTM/2)2t + 1000/(1+YTM/2)2t
YTM = 7%
For Dave Maturity = 19 years
Price = Coupont/(1+YTM/2)2t + Par Value/(1+YTM/2)2t
1000 = 35/(1+YTM/2)2t + 1000/(1+YTM/2)2t
YTM = 7%
If YTM increases by 2% so new YTM =9%
For Sam Maturity = 6 years
Price = Coupont/(1+YTM/2)2t + Par Value/(1+YTM/2)2t
Price = 35/(1+(9%/2)2t + 1000/(1+9%/2)2t
Price = 908.81
Percentage change in price of Sam bond = 908.81 -1000/1000 = -9.12%
For Dave Maturity = 19 years
Price = Coupont/(1+YTM/2)2t + Par Value/(1+YTM/2)2t
Price = 35/(1+9%/2)2t + 1000/(1+9%/2)2t
Price = 819.50
Percentage change in price of Dave bond = (819.50-1000)/1000 = -18.05%
If YTM decreases by 2% so new YTM =5%
For Sam Maturity = 6 years
Price = Coupont/(1+YTM/2)2t + Par Value/(1+YTM/2)2t
Price = 35/(1+(5%/2)2t + 1000/(1+5%/2)2t
Price = 1102.58
Percentage change in price of Sam bond = (1102.58 -1000)/1000 = 10.26%
For Dave Maturity = 19 years
Price = Coupont/(1+YTM/2)2t + Par Value/(1+YTM/2)2t
Price = 35/(1+5%/2)2t + 1000/(1+5%/2)2t
Price = 1243.49
Percentage change in price of Dave bond = (1243.49-1000)/1000 = 24.35%