A is 1.5 times as fast as B. A alone can do the work in 30 days. If A and B work on alternative days, beginning with A, in how many days will the work be completed? Choose the correct choice
A) 23
B) 22
C) 21
D) 36
E) 25
A can finish 1 work in 30 days   B can finish 1/1.5 work in 30 days - since A is 1.5 faster than B   This means   B can finish 1 work in 30*1.5= 
<gadget id="calculator">30*1.5</gadget>
<output>45</output>
45 days   Now using the awesome GMAT formula when two machines work together they can finish the job in= AB/ (A+B) = 45*30/(45+30) = 20*30/50 = 18 days   Since they alternate on days, it will take them double this time so total time = 18 * 2= 
<gadget id="calculator">18 * 2</gadget>
<output>36</output>
36 days   So answer is 36
<result>D</result>
A is 1.5 times as fast as B. A alone can do the work in 30 days. If A and B work on alternative days, beginning with A, in how many days will the work be completed?