To do a certain work alone 'a' takes 4 hrs. 'b' takes 5 hrs and 'c' takes 6 hrs. How long would a and b together take to do a work which c can do in 4.5 hrs?
a. 2 hrs 10 min
b. 2 hrs 30 min
c. 1 hr 20 min
d. 1 hr 40 min
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b.2hr 20 min I think it will be the answer
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