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08 Feb 2021, 03:15
Kudos
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E
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
75%
(hard)
Question Stats:
55% (02:29) correct
45%
(02:39)
wrong
based on 104
sessions
History
Date
Time
Result
Not Attempted Yet
Two cogged wheels of which one has 32 cogs and other 54 cogs, work into each other. If the latter turns 80 times in three quarters of a minute, how often does the other turn in 8 seconds?
A. 48
B. 42
C. 38
D. 32
E. 24
A. 48
B. 42
C. 38
D. 32
E. 24
16 Feb 2021, 01:42
Kudos
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Bunuel
Hi,
I know I was wrong on that one but I'd like someone to explain me why my reasoning is flawed :
I started with the 54-cog wheel : 80 turns every 45 seconds -> 16/9 turns per second.
Then, I focused on the 32-cog wheel : 32 * x = 54 with "x" being a multiplier to get 54 cogs from 32 cogs.
x = 27/8
Eventually, I multiplied 16/9 * 8 (because we are asked the number of turns per 8 secs) * 27/8 = 48 -> Answer A.
Anyone to correct me?
Thanks a lot !
16 Feb 2021, 04:38
Kudos
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Baps
The ratio between the bigger to smaller wheel is 54:32, which simplifies to 27:16. This can be written as 27/16.
This means that when the big wheel makes 1 turn, the small shall have made 27/16 turns.
If the big wheel makes 80 turns in 45 secs (3/4*60 secs), in 1 sec, it makes 80/45 turns i.e 16/9 turns. In 8 secs, it shall have made 16/9*8 turns.
The smaller wheel shall have made 16/9 * 8 * 27/16 =24 turns. Which is choice E
