Question 414788
Let {{{n+ 1}}} = number of passengers over 20 who 
must go in order to make the fare less than $7.50 per passenger
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The fare /passenger gets reduced by  exactly {{{9.5 - 7.5 = 2}}} dollars
if {{{n}}} passengers above 20 go.
The total number of passenger is {{{20 + n}}}
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{{{9.5*(20 + n) - .3n*(20 + n) = 7.5*(20 + n)}}} (normal cost) - (discount) = (desired cost)
{{{9.5 - .3n = 7.5}}}
{{{.3n = 2}}}
{{{n = 6}}} (nearest whole number)
{{{n + 1 = 7}}}
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If 26 people go, fare is {{{(9.5 - .3*6)*26 = 7.7*26}}} (fare/person)x(number of people)
If 27 people go fare is {{{(9.5 - .3*7)*27 = 7.4*27}}}  (fare/person)x(number of people)
It looks like 27 people must go to make fare less than $7.50 per person