The question asks me to calculate area under the graph. Seeing as gradient = -1, the x intercept is 60. The area under the graph would be 360, but this is wrong. Where is my mistake?
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1Are you sure the question doesn't ask for only the area specifically shown on the graph, which would be $(25-0)(12+7)/2=237.5$? – obscurans Jun 08 '20 at 11:30
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Check the scales: each vertical line is $5$ units apart, and each horizontal line is only $1$ unit apart. This makes the gradient $-\frac{1}{5}$. Splitting into a triangle and rectangle, I make the area to be: $$25 \times 1 + \frac{1}{2} \times 25 \times 5 = 87.5 \text{ units}^2.$$
user797616
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This isn't the area under the graph, since the question is asking to calculate area under the graph down to the x axis. Most of the area is not shown in the diagram. – oscar6721 Jun 08 '20 at 11:17
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@oscar6721 Are you also assuming that the area is bounded by the $y$-axis? – user797616 Jun 08 '20 at 11:18
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@oscar6721 Then, I also make the area $360 \text{ units}^2$. What makes you think this answer is incorrect? – user797616 Jun 08 '20 at 11:35
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It is an online worksheet, and as such the answers are checked automatically. I can't see any other possible answer, but the website says it is wrong. – oscar6721 Jun 08 '20 at 11:46
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You have different scales for $x$ and $y$. With equal units it seems as here:
As you can see, the gradient is not $-1$, but $-{1 \over 5}$.
MarianD
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I didn't phrase the question correctly - I know this and this is why I get 360 as my answer. – oscar6721 Jun 08 '20 at 11:24
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The area under the graph is $360$, if you mean that it is bounded by $x$-axis.
But in your picture it is bounded by lines $y=6$, $x=0$, and $x=25$, so the area in your picture is $87.5$. Maybe your task was to determine this area.
MarianD
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