Some geometrical exercises are a bit more difficult, owing to the context in which they're put (that is, because the math has been heavily wrapped in the "real world"); others are harder due to the complexity of the exercise statement (such as "two times that is three less than four times the other" kinds of phrasing).
Content Continues Below
These are the kinds of word problems for which being neat and organized, labelling things clearly, and taking your time can make the difference between fairly quick success and really lengthy frustration and possible failure.
Just give yourself permission to step back, decompress, and then dive in. You can totally do these.
The perimeter P of this rectangular area with (as-yet unknown) length L and width w is given by:
2L + 2w = 148
The area A is given by:
Advertisement
Affiliate
L × w = 1320
I will divide my perimeter equation above by 2, so I am dealing with smaller numbers. This gives me the following system (or set or collection) of equations:
L + w = 74
L × w = 1320
I can solve either one of these equations for either one of the variables, and then plug the result into the other equation for the other variable. I think I'll solve the addition equation for L in terms of w; then I'll plug the result into the multiplication equation:
L = 74 − w
(74 − w) × w = 1320
74w − w2 = 1320
0 = w2 − 74w + 1320
0 = (w − 30)(w − 44)
w = 30, 44
Once again, I've come up with two valid solutions. Neither is negative, so I can't discard either of them. I'll check each.
If w = 30, then:
L = 74 − w
= 74 − 30 = 44
If w = 44, then:
L = 74 − w
= 74 − 44 = 30
So, in this particular (and unusual) case, each of the solutions is valid; and taking one solution for the width will give the other solution as the length, and vice versa.
The important point is that the shorter side (whether I refer to it as the "width" or the "length") is the "narrow" side that is across the front of the lot.
garden dimensions: 44 ft by 30 ft
frontage length: 30 ft
Note that we cannot say which of the dimensions is the length or the width, since no information was provided regarding which was longer. So "this by that" is as accurate an answer as we can give.
Content Continues Below
The first statement, "three times the width exceeds twice its length by three inches", compares the length L and the width w. I'll start by doing things orderly, with clear and complete labelling:
the width: w
three times the width: 3w
twice its length: 2L
exceeds by three inches: + 3
equation: 3w = 2L + 3
The second statement, "four times its length is twelve more than its perimeter", compares the length L and the perimeter P. I will again be complete with my labelling:
four times its length: 4L
perimeter: P = 2L + 2w
twelve more than: + 12
equation: 4L = P + 12
I'll replace the perimeter variable with the expression (above) for the perimeter:
4L = (2L + 2w) + 12
Affiliate
So now I have my two equations:
3w = 2L + 3
4L = 2L + 2w + 12
There are various ways of solving this; the way I do it (below) just happens to be what I thought of first. I'll take the first equation and solve for w:
3w = 2L + 3
Now I'll simplify the second equation, and then plug in this above expression for w:
4L = 2L + 2w + 12
2L = 2w + 12
Then:
The question didn't ask me to "Find the values of the variables L and w". It asked me to "Find the dimensions of the rectangle," so my hand-in answer is:
length: 21 inches
width: 15 inches
URL: https://www.purplemath.com/modules/perimetr4.htm
© 2024 Purplemath, Inc. All right reserved. Web Design by