Consider a two-stage Carnot engine. In the first stage heat, Q1 is absorbed in temperature T and heat Q2 is expelled at temperature αT (where α < 1). In the second stage heat Q2 is absorbed at temperature αT and heat Q3 is expelled at temperature βT(β < α). The efficiency of the Carnot engine will be
1
1 − α − β
2
1 − α
3
1 − β
4
1 − αβ