is 13% the answer?

let m be the rate per month , then 1.15m is the rate per month after increase

let d be the number of days he used garage, then total cost assuming 30 days in month = md/30

let n be days to be reduced to remain at same cost, so we get

we need to find n*100/d

md/30 = 1.15m (d-n)/30

==>

d = 1.15(d-n)

divide both sides by d ==>

1 = 1.15 - 1.15n/d

==>1.15n/d = .15

==>100n/d = 15/1.15 = 13

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Thanks, Sri

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