Counting - ACT Math

Card 0 of 5

Question

How many irrational numbers are there between 3 and 7?

Answer

There is an infinite amount of irrational numbers between any two "real" (whole) numbers. 3 and 7 are both real numbers

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Question

How many prime numbers are between 20 and 50?

Answer

Prime numbers are numbers that cannot be divided evenly by any numbers besides itself and 1. The prime numbers between 20 and 50 are: 23, 29, 31, 37, 41, 43, 47, yielding an answer of 6.

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Question

3 candy bars and 4 bags of potato chips cost $7, and 3 candy bars and 2 bags of potato chips cost $5. What is the price of 1 bag of potato chips?

Answer

Increasing 2 bags of potato chips increases the cost by $2. Therefore, they cost $1 per bag.

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Question

How many integers are between and (not including and )?

Answer

The integers are .

So there are 8 integers total

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Question

What is the average of all prime numbers in between 7 and 23 (not including 7 or 23)?

Answer

A prime number is defined as any number that is only divisible by itself and 1 with no remainders. So for example, 7 and 23 are both prime numbers. Seven can only be divided by 7 and 1, any other number would give a fraction or decimal.

The best approach to this problem is to simply list each number starting from 7.

Seven itself is a prime number, but the question specifically says that 7 should not be included. Eight is divisible by 1, 2, 4, and 8, and therefore is not a prime number. Nine is divisible by 3 and so on. Quickly we see that the prime numbers in betwen 7 and 23 include:

Finally, the question asks you to find the average of these numbers:

Concepts such as prime numbers or other definitions should be readily called when taking the ACT with minimal effort.

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