a lab needs 200ml of a 5 salt solution they only have a 10 solution how much 10 solution and water should be mixed
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HESI A2

HESI A2 Math Portion

1. A lab needs 200ml of a 5% salt solution. They only have a 10% solution. How much 10% solution and water should be mixed?

Correct answer: B

Rationale: Rationale: 1. Let x be the volume of the 10% solution needed and y be the volume of water needed. 2. The total volume of the final solution is 200ml, so x + y = 200. 3. The concentration of the final solution is 5%, so the amount of salt in the final solution is 0.05 * 200 = 10g. 4. The amount of salt in the 10% solution is 0.1x, and the amount of salt in the water is 0, so the total amount of salt in the final solution is 0.1x. 5. Since the total amount of salt in the final solution is 10g, we have 0.1x = 10. 6. Solving for x, we get x = 100ml. 7. Substituting x =

2. Rebecca is able to paint 12 pickets on her picket fence in an hour. Her fence is 72 feet long, with 2 pickets per foot. How long will it take her to paint the fence?

Correct answer: B

Rationale: Rebecca can paint 12 pickets in 1 hour, which means she can paint 12 * 2 = 24 pickets in an hour. Since the fence is 72 feet long with 2 pickets per foot, she needs to paint a total of 72 * 2 = 144 pickets. If she paints 24 pickets per hour, it will take her 144 / 24 = 6 hours to paint the entire fence. Choice A (2.4 hours) is incorrect because it does not consider the total number of pickets on the fence. Choice C (12 hours) is incorrect as it overestimates the time needed based on her painting rate. Choice D (16.4 hours) is incorrect as it miscalculates the time required to paint the entire fence.

3. If the outside temperature is currently 15 degrees on the Celsius scale, what is the approximate temperature on the Fahrenheit scale?

Correct answer: A

Rationale: To convert Celsius to Fahrenheit, you can use the formula: (°C × 9/5) + 32 = °F. Substituting 15°C into the formula gives us (15 × 9/5) + 32 = 59°F. Therefore, the approximate temperature on the Fahrenheit scale for 15 degrees Celsius is 59 degrees Fahrenheit. Choice B, C, and D are incorrect as they do not align with the correct conversion formula and calculation.

4. What is the perimeter of a square with a side length of 5 meters?

Correct answer: B

Rationale: The formula to calculate the perimeter of a square is P = 4s, where P is the perimeter and s is the length of a side. Given that the side length is 5 meters, the perimeter is 4 * 5 = 20 meters. Therefore, the correct answer is B. Choices A (15 meters), C (25 meters), and D (30 meters) are incorrect as they do not correctly apply the formula to calculate the perimeter of a square.

5. If Larry can wash 50 cars in 20 minutes, how many minutes will it take him to wash 80 cars?

Correct answer: B

Rationale: To determine how many minutes it will take Larry to wash 80 cars, we first calculate his rate of washing cars per minute: 50 cars / 20 minutes = 2.5 cars per minute. To wash 80 cars, we divide the total number of cars by the cars washed per minute: 80 cars / 2.5 cars per minute = 32 minutes. Hence, it will take Larry 32 minutes to wash 80 cars. Choices A, C, and D are incorrect as they do not align with the correct calculation based on Larry's rate of washing cars.

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