now, the formula given gives the fraction for those still working, hence, the fraction for those not working is given by: 1 - (fraction of those still working)
this is 1 - f(1) = what the text says, well, the last 2 should be 3
after 2 years, f(2) still worked. after 3 years, f(3) still worked.b) What fraction of the toasters can be expected to fail during the third year of use?
thus the amount that failed during the 3rd year is f(2) - f(3) = what the text says