12 machines can do a work in 10days. How many machines are needed to complete the work in 40days? Choose the correct choice from the following answers:
A) 10
B) 3
C) 4
D) 7
E) 5
Required number of machines = 12*10/40= 
<gadget id="calculator">12*10/40</gadget>
<output>3</output>
3   Answer is 3
<result>B</result>
12 machines can do a work in 10days. How many machines are needed to complete the work in 40days?