Question

Dal and kim can assemble a swing set in 1.5 hours. working alone it takes kim 4 hour longer than dal how long will it take dal alone to assemble the swing set

Answer 1

dan's rate -- swing/x , where x is the numbers of hours to assemble the swing by himself
kim's rate --- swing/(x+4)

so swing/x + swing/(x+4) = swing/1.5
divide by "swing"
1/x + 1/(x+4) = 1/1.5
x+4 + x= (x)(x+4)/1.5
both sides times 3
6x+12 = 2x(x+4)
2x^2 + 2x - 12 = 0
x^2 + x - 6 = 0
(x-2)(x+3) = 0
x = 2 or a negative, which would be silly

Dal would need 2 hours to do the job himself