#1 Pat, Kate and Mark charged a total of 162 hours to a certain project. If Pat charged twice as much time to the project as Kate and 1/3 as much as Mark, how many more hours did Mark charge to the project than Kate?
let the hours charged by pat = p hours
let the hours charged by kate = k hours
let the hours charged by mark = m hours
p = 2k => k = p/2
p = m/3 => m = 3p
p+k+m = 162
so, p + p/2 + 3p = 162
solving for p we get p = 36
m = 3*36 = 108, k = 36/2 = 18
and m-k = 90
hope it is correct.