Answer is (1) 160 km in 2 hours and
(2) 16 miles in 12 minutes.
Step by step.
80 km / 1 hour = x km /2 hours
Cross multiply =
x = 160
The second one requires a little more math. Because we are looking at how far in minutes, we change the rate of 80km in 1 hour to 80 km in 60 minutes.
80 km / 60 = x / 12
Cross multiply
12x = 960
Solve for x by dividing both sides by 12
X = 16
I did the math on a print screen to explain the cross multiply.
1.8, Problem 37: A lidless cardboard box is to be made with a volume of 4 m3
. Find the
dimensions of the box that requires the least amount of cardboard.
Solution: If the dimensions of our box are x, y, and z, then we’re seeking to minimize
A(x, y, z) = xy + 2xz + 2yz subject to the constraint that xyz = 4. Our first step is to make
the first function a function of just 2 variables. From xyz = 4, we see z = 4/xy, and if we substitute
this into A(x, y, z), we obtain a new function A(x, y) = xy + 8/y + 8/x. Since we’re optimizing
something, we want to calculate the critical points, which occur when Ax = Ay = 0 or either Ax
or Ay is undefined. If Ax or Ay is undefined, then x = 0 or y = 0, which means xyz = 4 can’t
hold. So, we calculate when Ax = 0 = Ay. Ax = y − 8/x2 = 0 and Ay = x − 8/y2 = 0. From
these, we obtain x
2y = 8 = xy2
. This forces x = y = 2, which forces z = 1. Calculating second
derivatives and applying the second derivative test, we see that (x, y) = (2, 2) is a local minimum
for A(x, y). To show it’s an absolute minimum, first notice that A(x, y) is defined for all choices
of x and y that are positive (if x and y are arbitrarily large, you can still make z REALLY small
so that xyz = 4 still). Therefore, the domain is NOT a closed and bounded region (it’s neither
closed nor bounded), so you can’t apply the Extreme Value Theorem. However, you can salvage
something: observe what happens to A(x, y) as x → 0, as y → 0, as x → ∞, and y → ∞. In each
of these cases, at least one of the variables must go to ∞, meaning that A(x, y) goes to ∞. Thus,
moving away from (2, 2) forces A(x, y) to increase, and so (2, 2) is an absolute minimum for A(x, y).
Answer: Check if numbers are prime. Composite numbers prime factorization (decomposing, breaking numbers down to prime factors). Inscribe them as a product of prime factors, in exponential notation.
Answer:
Step-by-step explanation:
<u>Sides of the picture added margin:</u>
<u>Solution</u>:
- A(margin) = Total area - A(picture)
- (8 + 2x)(5 + 2x) - 5*8 = 30
- 4x² + 10x + 16x + 40 - 40 - 30 = 0
- 4x² + 26x - 30 = 0
- 2x² + 13x - 15 = 0
- x = (-13 + √(13² + 2*4*15))/4
- x = (-13 + 17)/4
- x = 1 cm
Note. The other root is ignored as negative.
Answer:
Step-by-step explanation:
Samantha needs 4/5 yard of fabric to make costumes for the school play.
Let x represent the number of yards of fabric that she has
Let y represent the total number of costumes that she can make from x yards of fabric.
Since one costume require 4/5 yards of fabric, y costumes will require
x ÷ 4/5 = x×5/4 = 5x/4
The equation will be
y = 5x/4
to find how many costumes she can make with 8 yards of fabric, it becomes
y = (5×8)/4
y = 40/4 = 10
