Qn) It takes Mr lim 7 hours to paint the room by himself. If Mr Tan helps him, they will take 3 hours to paint the room. How long will Mr Tan take to paint the room by himself?
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Its simple. Lim takes 7 hours means every hour he paints 1/7 th room.
They both do it in 3 hours mean they finish 1/3rd room in 1 hour.
So the Mr tan paints (1/3 - 1/7) = 4/21 part of room in 1 hour.
Which means he takes 21/4 hours to finish the job alone. (21/4 = 5 and a quarter hours)
They both do it in 3 hours mean they finish 1/3rd room in 1 hour.
So the Mr tan paints (1/3 - 1/7) = 4/21 part of room in 1 hour.
Which means he takes 21/4 hours to finish the job alone. (21/4 = 5 and a quarter hours)
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4 hours?