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If snow accumulation increased at a constant rate of 30 millimeters pe

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If snow accumulation increased at a constant rate of 30 millimeters pe  [#permalink]

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09 May 2018, 02:34
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Difficulty:

25% (medium)

Question Stats:

70% (01:09) correct 30% (01:14) wrong based on 109 sessions

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If snow accumulation increased at a constant rate of 30 millimeters per hour during a certain snowstorm, how many seconds did it take for snow accumulation to increase by 1 millimeter?

a) 1/120
b) 1/60
c) 1/20
d) 20
e) 120
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Re: If snow accumulation increased at a constant rate of 30 millimeters pe  [#permalink]

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09 May 2018, 06:08
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alanforde800Maximus wrote:
If snow accumulation increased at a constant rate of 30 millimeters per hour during a certain snowstorm, how many seconds did it take for snow accumulation to increase by 1 millimeter?

a) 1/120
b) 1/60
c) 1/20
d) 20
e) 120

Let's keep listing EQUIVALENT RATES until we get to 1 millimeter

30 millimeters per hour = 30 millimeters per 60 minutes
= 30 millimeters per 3600 SECONDS
= 3 millimeters per 360 SECONDS
= 1 millimeter per 120 SECONDS

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If snow accumulation increased at a constant rate of 30 millimeters pe  [#permalink]

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09 May 2018, 07:59
alanforde800Maximus wrote:
If snow accumulation increased at a constant rate of 30 millimeters per hour during a certain snowstorm, how many seconds did it take for snow accumulation to increase by 1 millimeter?

a) 1/120
b) 1/60
c) 1/20
d) 20
e) 120

I suspect the trap answer is A. It is easy to overlook units.

Shortcut: 1 hour = 3600 seconds
$$\frac{30mm}{1hour}=\frac{30mm}{3600secs}=\frac{1mm}{120secs}$$

Units are not the same. The answer is not A. In 120 seconds, 1mm of snow will accumulate.

No shortcut: $$(\frac{30mm}{1hour}*\frac{1hour}{60mins}*\frac{1min}{60secs})=\frac{30mm}{(60*60)secs}=\frac{30mm}{3600secs}$$

In the parentheses, hours and minutes cancel. Factor out 30, write the final units: $$\frac{1mm}{120secs}$$

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Re: If snow accumulation increased at a constant rate of 30 millimeters pe  [#permalink]

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10 May 2018, 09:40
alanforde800Maximus wrote:
If snow accumulation increased at a constant rate of 30 millimeters per hour during a certain snowstorm, how many seconds did it take for snow accumulation to increase by 1 millimeter?

a) 1/120
b) 1/60
c) 1/20
d) 20
e) 120

Recalling that 1 hour = 3600 seconds, we can create the equation:

30/3600 = 1/x

1/120 = 1/x

x = 120

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If snow accumulation increased at a constant rate of 30 millimeters pe  [#permalink]

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11 Sep 2018, 08:59
I haven't seen on GMATCLUB the method that I use (that I was taught in my school to convert ratios). I hope it will be helpful, at least it makes my life easier. See attachment below
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If snow accumulation increased at a constant rate of 30 millimeters pe &nbs [#permalink] 11 Sep 2018, 08:59
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