The total time he takes to assemble is 123 minutes.
What is Unitary method?
The unitary method is a technique for solving a problem by first finding the value of a single unit, and then finding the necessary value by multiplying the single unit value.
for second, 30*0.9=27
for third, 27*0.9 = 24.3
Similarly for the fifth computer,
=21.87*0.9
=19.68 minutes
Total time taken,
=30+ 27 +24.3+21.87+19.68
=122.553
=123 minutes.
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