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Jayvee's rate 1 letters in x minutes

Jun's rate 1 letter in y minutes

Jayvee can finish typing one letter ahead of Jun by one minute

x = y - 1

Together, they can finish 27 letters in 60 minutes

1/x + 1/y = 27/60

plug y = x + 1 into the last equation

1/x +1/(x + 1) = 27/60

by solving the equation we find

x = 4 minutes

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Jayvee needs 4 minutes ti finish typing one letter.