It takes jessica 1 hour 45 minutes to mow and trim the lawn. it takes felecia and jessica 1 hour to do the lawn. how long will it take felecia on her own?

This kind of problem request the use of harmonic mean:

if t₁ is the Time spent by Jessica, and
t₂, the time spent by Felecia, and t₃ the time spent by both, then the equation of that kind of problem will be:

1/t₁ + 1/t₂ =1/t₃.

t₁ = 1h45 min, t₂ (unknown, to be calculated), t₃ = 1 h, to ease things let' convert the time in minutes

t₁ = 105 min

t₂ = ?(time needed to Felicia to  maw the lawn)

t₃ = 60 min

1/105 +1/t₂ = 1/60===> 1/t₂ = 1/60 - 1/105==> 1/t₂ =1/140

& t₂ =140 minutes or t₂ = 2h & 20 min

1. 0.3 •4 is the same as 4 groups of 0.32. 7•0.8 is the same as 7 groups of 0.83. it increases by 0.5 every time, so 0.5x4 it increases by 0.9 every time, so 0.9x5. 0.9•12=10.86. 0.47•5=2.35i can finish the next ones in a separate post