A certain number of machines can do a work in 100days. If there were 10 machines more it could be finished in 10days less. How many machines are there? Choose the correct answer:
A) 50	B) 40	C) 90	D) 100	E) 60
Original number of machines = 10 * (100-10)/10= 
<gadget id="calculator">10 * (100-10)/10</gadget>
<output>90</output>
90 machines   Answer is 90
<result>C</result>
A certain number of machines can do a work in 100days. If there were 10 machines more it could be finished in 10days less. How many machines are there?