Question 634178
1/2.5 + 1/5 = 1/t


10/25 + 1/5 = 1/t


10t + 5t = 25 ... Multiply every term by the LCD 25t to clear out the fractions


15t = 25


t = 25/15


t = 5/3


t = {{{1&2/3}}}


So if they worked together, then it would take them {{{1&2/3}}} hours (or 1 hour, 40 minutes)