Robert needs 40 minutes to assemble a bookcase.Paul needs 20 minutes to assemble the same bookcase.
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Word Problems are normally set up using reciprocals.
x = time working together.
1/40 + 1/20 = 1/x
now clear denominators by multiplying all terms by all denominators and cross canceling like terms.
(40)(20)(x)[1/40+1/20] = (40)(20)(x)[1/x]
20x+40x = 40•20
60x = 800
x = 800/60
x ≈ 13.33 minutes
x = time working together.
1/40 + 1/20 = 1/x
now clear denominators by multiplying all terms by all denominators and cross canceling like terms.
(40)(20)(x)[1/40+1/20] = (40)(20)(x)[1/x]
20x+40x = 40•20
60x = 800
x = 800/60
x ≈ 13.33 minutes
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a half an hour about...