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Question
Math
Posted 10 months ago

Rohit is recapping his track season where he ran in a total of 24 races.
His coach tells him that 4 of his races were 100 meters in length and 2 races were 400 meters in length. He remembers that during the last 12 races of the season, he was expected to run a total of 4200 meters. He's also willing to assume that the lengths of these 12 races are representative of the rest of the races.

He isn't sure how many of the other races were 200 meters long and how many were 800 meters long.

Find the 2 missing numbers from the data table below.
\begin{tabular}{cc} 
Race length (meters) & Races \\
\hline 100 & 4 \\
200 & \\
400 & 2 \\
800 & \\
Total & 24
\end{tabular}
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Answer from Sia
Posted 10 months ago
Solution by Steps
step 1
Combine the known quantities of races and the total number of races to express the unknown quantities in terms of each other
step 2
Using the equation 24=4+x+2+y24 = 4 + x + 2 + y, solve for xx in terms of yy: x=18yx = 18 - y
step 3
Combine the distances run in the last 12 races to express the unknown distances in terms of each other
step 4
Using the equation 4200=12/2×(4×100+x×200+2×400+y×800)4200 = 12/2 \times (4 \times 100 + x \times 200 + 2 \times 400 + y \times 800), solve for xx in terms of yy: x=4y5/2x = -4y - 5/2
step 5
Substitute x=18yx = 18 - y from step 2 into the equation from step 4 to find the value of yy
step 6
Solve the resulting equation to find the number of 800m races (yy)
step 7
Substitute the value of yy back into the equation x=18yx = 18 - y to find the number of 200m races (xx)
[question 1] Answer
x = number of 200m races, y = number of 800m races
Key Concept
System of Equations
Explanation
To find the missing numbers of races, we set up a system of equations based on the total number of races and the total distance run in the last 12 races. We then solve this system for the unknowns.
Solution by Steps
step 1
Combine the known quantities of races and the total number of races to express the unknown quantities in terms of each other
step 2
Using the equation 24=4+x+2+y24 = 4 + x + 2 + y, solve for xx in terms of yy: x=18yx = 18 - y
step 3
Combine the distances run in the last 12 races to express the unknown distances in terms of each other
step 4
Using the equation 4200=12/2×(4×100+x×200+2×400+y×800)4200 = 12/2 \times (4 \times 100 + x \times 200 + 2 \times 400 + y \times 800), solve for xx in terms of yy: x=4y5/2x = -4y - 5/2
step 5
Substitute x=18yx = 18 - y from step 2 into the equation from step 4 to find the value of yy
step 6
Solve the resulting equation to find the number of 800m races (yy)
step 7
Substitute the value of yy back into the equation x=18yx = 18 - y to find the number of 200m races (xx)
[question 2] Answer
x = number of 200m races, y = number of 800m races
Key Concept
System of Equations
Explanation
To find the missing numbers of races, we set up a system of equations based on the total number of races and the total distance run in the last 12 races. We then solve this system for the unknowns.

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