PSAT/SAT & ACT Math Attack – Two Problems Today

Hurray Math

1) 2 times a certain number is 4 less than the number, what is the number?

    1. -4
    2. -2
    3. 1
    4. 2
    5. 3

 

Explanation: The first step is to express what you see in words in a mathematical equation you can actually solve.

(2 x n) = n – 4

After expressing the problem, try to simplify it as much as possible:

2n = n ­– 4

From here, it is simply a matter of dividing by n:

2n/n = (n – 4)/n

                n = -4

The answer is thus (A).

That question was easy, so today we’re going to give you two:

2) The average (arithmetic mean) of three numbers is equal to 50. If one of the numbers is 10, what is the sum of the other two numbers?

    1. 40
    2. 90
    3. 100
    4. 140
    5. 150

Explanation: If the arithmetic mean of three numbers is 50, then the sum of those three numbers is 150:

x/3 = 50

x = 150

If the sum of three numbers is 150, and we know that one of those three numbers is 10, then we know the sum of the other two numbers must be 140:

10 + y +z = 150

y + z = 140

The answer is thus (D).

Have a question? Ask the experts at Test Masters!
Have a question? Ask the experts at Test Masters!

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