Quick QR Question Plz Help

[RozhonDDS]

I know this question appears on a lot of DAT exams and it seems pretty simple, but i am not sure why i can't get the right answer

One pump can fill a vat in 10 mins. Another pump can fill a vat in 15 mins. How many minutes, does it take to fill the vat if both pumps are operating at the same time?

A. 1/6
B. 6
C. 12
D. 12.5
E. 25

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[dat_student]

I know this question appears on a lot of DAT exams and it seems pretty simple, but i am not sure why i can't get the right answer

One pump can fill a vat in 10 mins. Another pump can fill a vat in 15 mins. How many minutes, does it take to fill the vat if both pumps are operating at the same time?

A. 1/6
B. 6
C. 12
D. 12.5
E. 25

Easy, this is the general formula for any parallel operation:
1/R = 1/R1 + 1/R2

1/R = 1/10 + 1/15
1/R = (10 + 15)/(10 * 15) = 25/150 = 1/6
R = 6
B is the right answer

To double check:
6 < 10 & 6 < 15
You can automatically cross C, D, E because none of those is smaller than the smallest number in the set {10 min, 15 min}
Without doing any math you should be able to tell B is obviously the answer. A is just too small.
I have some classes to teach. I'll be back later this evening. If you have any more questions feel free to send me a pm.

 

[BirkChick]

I know this question appears on a lot of DAT exams and it seems pretty simple, but i am not sure why i can't get the right answer

One pump can fill a vat in 10 mins. Another pump can fill a vat in 15 mins. How many minutes, does it take to fill the vat if both pumps are operating at the same time?

A. 1/6
B. 6
C. 12
D. 12.5
E. 25

Hey -- my way of doing these problems may be a bit quicker and easier for you!

First, I come up with a vat size that is divisible by both times, in this case the vat size would be 30 gallons (units are arbitrary).

Then, I find the filling rates of each pump: 30gal/10min = 3 gal/min; 30gal/15min = 2 gal/min.

Now that you have the rates, you can add them and determine how long it will take to fill a 30 gallon vat with both running: 30gal/(3+2) = 6 minutes.

Good luck!

 

[luder98]

Easy, this is the general formula for any parallel operation:
1/R = 1/R1 + 1/R2

1/R = 1/10 + 1/15
1/R = (10 + 15)/(10 * 15) = 25/150 = 1/6
R = 6
B is the right answer

To double check:
6 < 10 & 6 < 15
You can automatically cross C, D, E because none of those is smaller than the smallest number in the set {10 min, 15 min}
Without doing any math you should be able to tell B is obviously the answer. A is just too small.
I have some classes to teach. I'll be back later this evening. If you have any more questions feel free to send me a pm.

This is the way to solve this type of problems. Just memorize the formula and plug in the numbers, no thinking. Better yet, just memorize the derived formula: Overall Rate = Product/Sum. Note that this formula only applies to two pumps or persons. If you have more than 2, then you'll have to use the original formula. That, however, is very rare on the DAT.

 

[tinman831]

Both methods that were listed are the exact same method. Dat_student provided actual algebraic formulas, whereas birkchick used words to describe it. Both methods are the same but it might be better to memorize the formulas so you can recall it easier during the exam.