**Answer to Problem #20:
**

**This is a 'parallel' problem solved by
a formula (derived in the text):
**

To simplify computation, the above formula can be reworked to: Tt =1=1+1where: Tt = time for job (together) Tt T1 T2 T1 = time for job (1st person alone) T2 = time for job (2nd person alone)T2 = 90 days (ANSWER)T1 x T2T1 + T2 30 =45 x T245 T2 = 30 (45 + T2) = 1350 + 30 T2 45 + T2 45 T2 - 30 T2 = 1350 15 T2 = 1350 T2 = 1350 / 15return