Hope i am right.
Call Plan = 25 $
Regular chrages = 1.6 $ ( for first 3 min) + 0.8 ( each additional min )
For a call of 60 min RC 1 = 1.6 + .8 * 57 = 47.2
The customer could maximize his saving by making calls of 3 min since be only charged for 1.6. So for 60 min he can make 2o calls
For a call of 60 min RC 2 = 1.6 * 20 = 32
Saving S1 = 47.2 - 32 = 15 . 2
Inspite of this he hets a 40 % discount
RC1 = 47.2 * .6 = 28.32
RC2 = 32 * .6 = 19.2
Saving S2 = 28.32 - 19.2 = 9.12
Total Saving = S1 + S2 = 15.2 + 9.12 = 24.32
I feel the right answer should be $18.88, which is not listed above. This is a very poorly worded question.
Asking for maximum savings on a 40% discount is basically asking what is the maximum charge that can be racked up, i.e. 40% of maximum charges will lead to maximum savings.
While there is nothing wrong with your math, there is an issue of classification.
Saving S1 = 47.2 - 32 = 15 . 2 <-- How is this a saving? The regular charge is $1.60 for the first three minutes. Making 20 three min calls instead of one long hour call is just exploiting the regular charge, it should not count as a savings.
The question phrases the situation as a single saving, that one can save 40% on regular charges. If the question wishes to clarify that there are two types of saving, the first ($1.60 for the first three minutes) should NOT be listed under regular charges. Paying regular charges should NOT count as savings.
I feel this is a poorly worded question.