An algebra problem by A Former Brilliant Member
Algebra
Level
2
Marvin and his brother can dig a well if Marvin works in 12 hours and his brother in 6 hours or they can do it if Marvin works in 8 hours and his brother in 9 hours. How long will it take Marvin to dig the well alone?
19
18
21
20
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1 solution
Observe that as we increase Marvin's contribution by 4 hours, his brother's contribution decreases by 3 hours.
Working from "Marvin 12 hours, brother 6 hours", we must decrease his brother's contribution by 2 × 3 .
Therefore Marvin's contribution must increase by 2 × 4 .
1 2 + 2 × 4 = 2 0 .