Vlad spent 20 minutes on his history homework and then completely solved x math problems that each took 2 minutes to complete. What is the equation that can be used to find the value of y , the total time that Vlad spent on his homework, and what are the constraints on the values of x and y ?
Answer
A
y is equal to 2 x plus 20 ; x is any integer greater than or equal to 0 , and y is an integer greater than or equal to 20 .
B
y is equal to 2 x plus 20 ; x is any real number greater than or equal to 0 , and y is any real number greater than or equal to 20 .
C
y is equal to 20 x plus 2 ; x is any integer greater than or equal to 0 , and y is an integer greater than or equal to 20 .
D
y is equal to 20 x plus 2 ; x is any real number greater than or equal to 0 , and y is any real number greater than or equal to 20 .
Explanation
The history homework took 20 minutes, and the math homework took 2 minutes for each of x problems. So the total time is y = 20 + 2x. Since Vlad completed a whole number of problems, x must be a nonnegative integer. The total time is therefore also an integer of at least 20 minutes, matching choice C.
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