Monday

October 5, 2015
Total # Posts: 11,340

**Math**

Let the circle pass through, in general, three points: (x1,y1) (x2,y2) (x3,y3) and the equation is to be expressed in the form x²+y²+dx+ey+f=0 The required equation may be expressed in determinant form: [y^2+x^2, x, y, 1] [y1^2+x1^2, x1, y1, 1] [y2^2+x2^2, x2, y2, 1...
*June 6, 2014*

**Statistics**

Normal distribution table give μ+2.33σ as the 99% level. Calculate the warranty period accordingly. Tell me which brand it is that has 40 years mean life! :)
*June 6, 2014*

**probability**

You're welcome!
*June 6, 2014*

**probability**

Calculate the probability that the building is protected by NO alarm. Subtract from 1.0 gives you the probability required. P(≥1)=1-(1-80%)*(1-70%) Let P(W)=x Probability of picking two whites P(WW)=x²=0.49 x=?
*June 6, 2014*

**Statistics - correction**

Last line should read 29/111
*June 6, 2014*

**Statistics**

Assuming leading zeroes count as digits, then probability of seeing 3 distinct digits = 10*9*8/1000 = 720/1000 =18/25 Probability of at least 2 identical digits = 280/1000 =7/25 If leading zeroes are not displayed, then there are 9*9*8=648 plates with distinct digits between ...
*June 6, 2014*

**trig**

Work done =F.D =F*D*cos(θ) =<0,-3400><1000sin(8°),1000cos(8°)> =3400000cos(8°) ft-lb (gravitation units)
*June 6, 2014*

**MATH**

Use the slope equation: slope = (y2-y1)/(x2-x1)
*June 5, 2014*

**Physics**

F=<-3,-7.6> Δr = <3.6,-2> Work done F.Δr = <-3,-7.6><3.6,-2> = 4.4 J
*June 5, 2014*

**algebra**

It is almost a linear function, if the 8 becomes a 9, i.e. the y-values become -7,1,9,17,25. Otherwise the answer is no.
*June 5, 2014*

**Physic**

At the beginning, the box is in uniform rectilinear motion (URM), which means that the horizontal force is just enough to balance the frictional resistance, where Pushing force, F =Frictional resistance = μkmg = 0.3 mg With increase in coefficient of friction, the net force...
*June 5, 2014*

**Physics**

We know that the intensity of the omnidirectional source is proportional the energy rate and inversely proportional to the square of the distance (inverse square law). So 1/8² = 0.5/d² Solve for d.
*June 5, 2014*

**Physics**

The magnitude |<x,y>| of a vector given as <x,y> can be obtained by a calculation similar to Pythagoras theorem. For example, |<3,4>| = sqrt(3²+4²)=5 The direction θ with respect to the x-axis can be calculated using a calculator by: θ=...
*June 4, 2014*

**physics**

Equate energy with the heat of fusion of water. (1/2)mv²=MH m=mass of bullet(kg) H=heat of fusion (J/kg) M=mass of ice melted (kg) Make sure the heat of fusion of water is converted to J/kg for your calculations.
*June 4, 2014*

**physics**

Use ΔQ=mcΔT where Q=heat in joules m=mass in kg T=temperature in °C c=specific heat in J/(kg-°C)
*June 4, 2014*

**physics**

One MW (megawatt) is 1 million watts. One watt is 1 joule / second. If the plant efficiency is 34%, it means that 34% of the energy is converted into electricity, while (100-34)=66% is dissipated as heat. So calculate the power converted to heat, and use the conversions above ...
*June 4, 2014*

**physics**

10 cos(60°)
*June 4, 2014*

**Math**

p=P(B)=0.77 q=1-P(B)=0.23 = probability of walking n=5 (days) r=3 days taking bus Given independence of choice from day to day, and probability does not vary, then we can use the binomial distribution. To calculate the probability of taking the bus exactly r days out of n: P(n...
*June 4, 2014*

**c++**

Here's a sample pseudocode. Input initial populations, p1, p2. Input growth rates, r1,r2. Input number of years to print, n. for year=0 to n output year, p1*pow(1+r1,year), p2*pow(1+r2,year) next year If you have problems getting your code to work, post your code.
*June 4, 2014*

**Geometry - need more information**

Please complete the description of the diagram and the questions.
*June 4, 2014*

**10**

Nice problem. Let ABC be the right-triangle, right-angled at C, such that AC=12, BC=6. Let the "inscribed" square share a common right-angle at C, and meet the hypotenuse AB at D. Let E be a corner of the square on AC, and F be a corner of the square on BC. Let x ...
*June 4, 2014*

**Probability**

The outcome consists of individual answers of true/false, probability remains constant throughout, use Binomial probability. P(n,r,p)=nCr*p^r(1-p)^(n-r) n=size of sample r=(exact)number of outcomes each with probability of p At most 2 means 0,1 or 2. The answer is P(20,0,0.05...
*June 4, 2014*

**Algebra**

Here we see that x cannot be zero, so replace (1/x) by y and solve the resulting quadratic. 6y²-7y+2=0 (2y-1)(3y-2)=0 y=1/2 or y=2/3 find x from y=1/x, or x=1/y x=2, or x=3/2
*June 4, 2014*

**Algebra**

BEDMAS tells us that exponents are evaluated before division, so the equation reads (x²)/5 + x/5-6=0 Multiply by 5 to get x²+x-30=0 (x-5)(x+6)=0 So x can be readily found.
*June 3, 2014*

**physics**

Distance = total of distances =10+10=20 m. average speed = total distance / total time = (30+50)/(10+30) m/s = ?
*June 3, 2014*

**Physics I NEED HELP WITH EQUATIONS**

Assuming the block is on a horizontal surface. Vertically (y): Gravitational force = mg normal reaction, N = mg (N is reaction required to remain in equilibrium) Horizontally (x): Since block moves with constant velocity, it is in dynamic equilibrium, so for equilibrium, ...
*June 3, 2014*

**math**

Let x=interest, 4000:280 = P : x converts into the equation 4000/280 = P / x which when cross multiplied gives 4000x = 280P divide both sides by 4000 to get: x(interest) = (280/4000)P =(7/100)P or =0.07P
*June 3, 2014*

**math**

See: http://www.jiskha.com/display.cgi?id=1401846779
*June 3, 2014*

**physics**

Using the idea of resistors in series and in parallel, we conclude that: resistance is proportional to length, and inversely proportional to the area. That should be sufficient to solve the first problem.
*June 3, 2014*

**linear math**

Expand the both sides of the equal sign and compare. If both sides are identical, it is an identity, i.e. equality for all values of x. If the two sides are not identical, it is an equation, valid only for certain values of x. For example, 5(x+2)=5x+10 expand 5x+10=5x+10 both ...
*June 3, 2014*

**Geometry**

If B is mid-point, then AB=10 = 2x+5=BC or x=2.5 then AC=20=8x and not 5x. So it is not possible.
*June 3, 2014*

**Physics**

That's correct!
*June 3, 2014*

**Physics**

Power = VI, compatible units are W, V, A. 10 kW = V(20 A) NOTE: 10 kW = 10000 W
*June 3, 2014*

**Physics**

Req =1/(1/R1+1/R2+1/R3+...) So, with 3 resistors, Req =1/(1/5+1/2.5+1/10) =...
*June 3, 2014*

**Physics**

Do you mean one 10Ω is in series with two 10Ω in parallel? the ones in parallel are worth 5Ω so the total equivalent resistance is 10+5=15. Use V=IR
*June 3, 2014*

**MATH**

Equation of line? y=(3/2)x+3
*June 3, 2014*

**Physics**

Correct!
*June 3, 2014*

**Physics**

The equivalent resistance, R =1/(1/10+1/20)=1/(3/20)=20/3 Ω Use V=IR to find the current.
*June 3, 2014*

**Geometry**

The area of parallelogram is Area=a*b*sin(θ) where a, b are adjacent side lengths, and θ is the included angle.
*June 3, 2014*

**Geometry**

Sorry. In that case, we make use of the fact that rhombuses have diagonals which intersect at right-angles. Thus each side is the hypotenuse of a right triangle with legs equal to the half-diagonals. Thus if s=length of each side of the rhombus, then s²=(AC/2)²+(BD/2...
*June 3, 2014*

**Geometry**

A quadrilateral with all four sides equal is a rhombus, whose area is half the product of the diagonals AC and BD.
*June 3, 2014*

**physics**

weight = 11.2 N = mg => m=11.2/9.8 = 1.143 kg new weight = 13.1 = m(g+a) a=13.1/1.143-9.8=1.661 m/s²
*June 3, 2014*

**math -logarithm**

729=9³ log9729 = 3 25 = (1/5)-2 log(1/5)25 = -2 for a=bc² rearrange to (a/b) = c² and proceed similar to above.
*June 3, 2014*

**math -logarithm**

x=log1010000 10x=10000 therefore x=4, or log1010000=4
*June 3, 2014*

**Math - Data Management**

Binomial distribution gives us 5C2*(.5)²(.5)³ =10(.5)^5 =0.3125 E(x)=2400*0.3125=750
*June 3, 2014*

**physics**

vf=vi+at a=-0.08 m/s² vi=1 m/s t=4 s
*June 3, 2014*

**physics - insufficient information**

Graph is a necessary ingredient of this question.
*June 3, 2014*

**physics**

Δx = vi*Δt+(1/2)aΔt² vi=0 so Δx = (1/2)aΔt² a=2Δx/Δt² =2*420/(32²) =(105/128) m/s² vf=aΔt =(105/128)*32 =26.25 m/s (not extremely fast for a plane)
*June 3, 2014*

**Physics :)**

You're welcome!
*June 3, 2014*

**Physics**

Correct.
*June 3, 2014*

**physics**

Her resultant speed is perpendicular to the flow of the river. Thus resultant velocity, using Pythagoras theorem, V=√(1.2²-0.8²) =√(0.8) =0.8944 m/s Time to cross river =550m/0.8944 m/s =614.9 s =10 minutes 15 seconds, approx. to cross as rapidly a ...
*June 3, 2014*

**Physics - correction**

Power = VI watts
*June 3, 2014*

**Physics**

V=IR I=V/R=45/15000=3*10-3 A. Power = VI joules
*June 3, 2014*

**statistics**

min/max number of people hired =50,80 Best estimate of number of people hired =(50+80)/2=65 Best estimate of people who speak English only = 0.75*65=48.75, or approx. 49 persons Note that sometimes the "best estimate" is interpreted as mean, which often is the best ...
*June 3, 2014*

**Math**

Assuming the question requires the zeroes of Y(x). Multiply by 50 (to get integer coefficients) 50*y(x)=-x²+65x+400=0 Solve by quadratic formula: x=(-65±√(65²+1600))/-2 =5.66 or 70.66 approximately
*June 3, 2014*

**statistics**

If all students take at least one of the subjects, then no one took both, because 84+16=100.
*June 3, 2014*

**Physics**

Area swept by turbine = 2000 m² Wind speed, v = 10 m/s mass of air through turbine, m = Volume of air * density = 2000 m² * 10 m/s * 1.3 kg /m³ = 26000 kg/s Raw power = kinetic energy available /s = (1/2)mv² = (1/2)*26000 kg/s * (10 m/s)^2 J/s = 1.3 MW With...
*June 3, 2014*

**math HELP!!!!!!**

This is an experimental probability project. Ideally you will need a 10-sided die (can get from toy/game stores) in the shape of a duodecahedron (10 identical faces), and proceed as described. The more trials you make, the closer it should approach the expected values, i.e. 10...
*June 2, 2014*

**Physics HELP ME PLEASE**

Newton's second law says "Force = mass × acceleration". Here acceleration = (27-11)/5.4 m/s² mass = 1250 kg So you can find the force accordingly.
*June 2, 2014*

**math :)**

You're welcome!
*June 2, 2014*

**math**

Assuming you mean A= -3(a + b - (1/3)c) when parentheses are used correctly. Divide both sides by -3, and swap sides a+b-(1/3)c = -A/3 -(1/3)c = -A/3-a-b Divide both sides by -(1/3) c = A+3a+3b
*June 2, 2014*

**Physics I NEED HELP BADLY :)**

You're welcome!
*June 2, 2014*

**Physics I NEED HELP BADLY**

Airplane speed = <270,0> (components in the x,y directions) Wind speed 75 km/hr eastwards =<75,0> Resultant speed = <270,0>+<75,0> = <345,0> = 345 km/hr eastwards. Wind speed blowing 75 km/h west Resultant =<270,0>+<-75,0> =<195,0&...
*June 2, 2014*

**physics**

If the acorn fell from rest, equate energies mgh=(1/2)mv² h=v²/2g =100/(2*9.8) =5.1 m Time =v/g =10/9.8 =1.02 s
*June 2, 2014*

**Physics**

Assuming it is a 20 m bridge. Initial vertical velocity = 0 time to reach base = t then t=√(-2Δy/g) =√(2*20/9.8) =2.02 s Horizontal distance =2.02*35 m/s =70.7 m approximately
*June 2, 2014*

**Physics**

Distance between wave crests, λ = wave length = 2 metres Time complete one wave = period = 60 s / 20 waves = 3 s Frequency f is number of waves per second = (1/3) Hz Speed = f * λ = (1/3)Hz * 2m =2/3 m/s
*June 2, 2014*

**Algebra**

Next easiest is by comparison. Solve the quadratic by factoring -3x+5 = x² +2x -45 x²+5x-50=0 (x+10)(x-5)=0 x=5 or x=-10 Substitute x to find corresponding values of y.
*June 2, 2014*

**Algebra**

Find the vertex of the parabola by completing the square: h(t)=-16t²+20t+6 =-16(t²-2(5/8)t+25/64)+6+25/4 which means that the vertex is at t=5/8 and it will hit the ground at h(t)=0, or t=3/2 s (rejecting negative root). Maximum is at the vertex, or h(5/8)=49/4 ft.
*June 2, 2014*

**Which one is correct?**

Eden is right. Multiplying two numbers with the same base is the same as adding the exponents.
*June 2, 2014*

**Algebra/can you help me**

log710 =log(10)/log(7) =1.183294662454939 approximately (use your calculator) I'll leave the other problem for you to practise.
*June 2, 2014*

**physics**

Some characters are not properly displayed on my computer, I assume it to be: A particle moves along the x-axis from an initial position xi to a final position xf. Of the following values of xi and xf, which results in a negative displacement? (a) xi = 6 m, xf = 4 m (b) xi = -...
*June 2, 2014*

**Math**

The starting number (initial value, or y-intercept) is not subject to the power, so the rule for the function is y=2(3)^x year 0: 2(3)^0 = 2 year 1: 2(3)^1 = 6 year 2: 2(3)^2 = 18 ... year 6: 2(3)^6 = 1458
*June 2, 2014*

**Math**

{L,M} is the Ω (sample space) for one single draw. When there are two draws one after another with replacement, the sample space will contain LL LM ML MM
*June 2, 2014*

**Physics**

Ignoring air resistance, equate potential and kinetic energies: mgh = (1/2)mv² Cancel m, v=√(2gh) =√(2*9.8*15) = 17.1 m/s
*June 2, 2014*

**science**

Please look up a diagram of the parts and then give a try at the answer.
*June 2, 2014*

**geometry**

The area can be found by using cross multiplication of elements in a rectangular matrix formed by the coordinates of the 4 (or any number) points. Let P be a 5x2 matrix, where the columns represnt the x and y coordinates. Rows 1 to 4 represent the (x,y) ordered pairs of the 4 ...
*June 2, 2014*

**physics**

Gravity acts on bodies of mass m with a force of mg equal to its weight. g is the acceleration due to gravity. The given weight is 10N, so gravity is already included, and the net force acting on the table is 10N.
*June 2, 2014*

**rounding to the nearest meter**

51 is the nearest metre, and 51.4 is the nearest tenth of a metre.
*June 2, 2014*

**jill**

Future value, F = 5*125000=625000 Interest, i = 6% annually = 0.06 compounding frequency, f = 2 Time, t = 2.5 years Let P = present value then use the compound interest formula F=P(1+i/f)ft Solve for P P=F/(1+i/f)ft =625000/(1+0.06/2)2*2.5 =539130.49 =
*June 2, 2014*

**Kirr**

Please do not use more than one name for your posts.
*June 1, 2014*

**jill**

Isn't 1500 already the present value? Could you double check to see if there is a typo?
*June 1, 2014*

**physics**

Distance = speed * time = (1.25*speed)*((1/1.25)*time) = 25 min./1.25 = 20 minutes
*June 1, 2014*

**helppppp math helppp!**

Future value, F Interest, i = 0.045 compounding frequency, f = 12 Time, t = 3.5 years Let P = present value, = 250000 then use the compound interest formula F=P(1+i/f)ft
*June 1, 2014*

**physics**

Horizontal component of the normal force.
*June 1, 2014*

**Physics**

Use Ek=(1/2)mv² Equate Ek=mgh h=height
*June 1, 2014*

**Physics**

Good, so Frictional force = ma = 1kg (-2.5)m/s² = -2.5 N Normal reaction =mg =1kg * 9.8 m/s² =9.8 N Coefficient of kinetic friction = Frictional force / Normal reaction = -2.5 / 9.8 = 0.255 (omit sign).
*June 1, 2014*

**trigonometry, check my answer please?**

It doesn't sound right when you have a 15 ft. ladder leaning against a wall with the foot of the ladder 36.9 ft away. So you need to recheck your work when it does not look right. The length of the ladder is the hypotenuse of the right triangle. The base of the ladder is ...
*June 1, 2014*

**Math**

Work on the left-hand side first: csc60 cot30 tan60 =(1/sin60)(tan60)(tan60) =(1/sin60)(tan²60) =(1/sin60)(sec²60-1) =(2/√3)(2²-1) =2√3 Work on the right-hand side: 2sec²45cos30 =2(2/√2)² (√3)/2 =8/2 (√3)/2 =2√3 Thus...
*June 1, 2014*

**Geometry :)**

You're welcome!
*June 1, 2014*

**Geometry**

Assuming my interpretation of the word "back" is correct, I said: "... because we usually consider the positive x-axis as going forward" so it would be A.
*June 1, 2014*

**Geometry**

A sphere has infinite planes of symmetry, a cube does not. All the given choices (A) to (C) are solids. A polygon is a plane figure. We cannot make a solid out of plane figures. We can make faces of polyhedrons out of plane figures, but that's not what the question is ...
*June 1, 2014*

**Geometry**

If you notice that all the coordinates of the image are half the corresponding values in the pre-image, this means that the transformation is a contraction about the origin, with a factor of 0.5.
*June 1, 2014*

**Algebra 1**

Slope of segment, a = (y2-y1)/(x2-x1) = (8-4)/(6-2)=1 Mid-point =( (x1+x2)/2, (y1+y2)/2 ) =( (2+6)/2, (4+8)/2 ) = M(4,6) Slope of line perpendicular to segment,a1 = -1/a = -1/(1) =-1 Equation of perpendicular line: (y-y1)=a1(x-x1) y-6 = -1(x-4) or y=-x + 10 Check that it goes ...
*June 1, 2014*

**Math**

For every 100 people, there were 40 men 30 women 30 children. Use proportion to figure out the number for 2400 people.
*June 1, 2014*

**Algebra**

Sum and difference: (sum+difference)/2 = larger number (sum-difference)/2 = smaller number
*June 1, 2014*

**math**

1 foot = 0.3048 m (exactly) so 1 m² = (1/0.3048)² ft². Area of rectangle = 48 m × 24 m = 1152 m² = 1152/0.3048² ft² = 12400.0 ft² (approximately)
*June 1, 2014*

**Physics**

The picture is not complete. Are the two blocks identical (in mass) ? Does block B hang free? If it is, B will descend as A moves up. Draw the free body diagram of each block. Let the tension in string be T. mass of each block = m acceleration due to gravity = g angle of ...
*June 1, 2014*

**biology Please Help**

I am not a biology expert, but here are some mathematical aspects of the problem. If both parents are heterozygous (contains one PKU allele, or Pp), the outcomes are: PP has PKU (probability 1/4) Pp carrier pP carrier pp non-carrier (probability 1/4) Probability of being a ...
*June 1, 2014*

**physics**

Round trip distance is double the earth-moon distance. Speed of light is 3*10^8 m/s. Distance = Speed * time, so Time = Distance /Speed Plug in numbers and calculate time accordingly.
*May 31, 2014*

**Pre-Calculus**

If you mean to find the value of cos(2θ) given cos(θ)=7/13, then use the double angle formula: cos(2θ)=cos²(θ)-sin²(θ) where: sin²(θ) =(1-cos²(θ)) =120/169
*May 31, 2014*