Roll a pair of dice until it lands doubles. What is the probability you will get the first doubles within three rolls? (Correct to four decimal places.)What is the probability it will take between 5 and 7 rolls?

Probability of rolling doubles in first three roles = 0.4124

Probability of it taking between 5 to 7 rolls = 0.1988

Step-by-step explanation:

Let's start by the total number of possible outcomes. This is 6 for one dice, and 6 for the other. So in total that's 6 x 6 = 36 different outcomes of the dice roll.

The number of ways we can roll a double is 6.

So the probability of rolling a double would be the number of ways to roll a double divided by the total possible outcomes.

This is : = 0.1667

The probability of NOT rolling a double: 1 - 0.1667 = 0.8333

Since the probability of rolling a double is equal to 1 - probability of not rolling a double, we can answer the first question in the following way.

The probability of NOT rolling a double for the first THREE turns:               0.8333 x 0.8333 x 0.8333 = 0.5786

Probability of rolling a double in first THREE turns: 1 - 0.5786 = 0.4124

The probability it will take between 5 to 7 rolls would be:

EQUATION 1: (probability of rolling no doubles in first 4 turns) x (probability of rolling a double in the next three turns)

Since we have already found the probability of rolling a double in three turns to be 0.4124, all we need to find is the probability of NOT rolling a double in the first four turns.

This is: 0.8333 * 0.8333 * 0.8333 * 0.8333 = 0.4822

Plugging this into EQUATION 1 we get: 0.4822 * 0.4124 = 0.1988

answer: learning objective(s)

·         describe the creation and use of systems of equations.

·         graph a system of linear equations on the coordinate plane and identify its solution.

introduction

sometimes graphing a single linear equation is all it takes to solve a mathematical problem. other times, one line just doesn’t do it, and a second equation is needed to model the situation. this is often the case when a problem involves two variables. solving these kinds of problems requires working with a system of equations, which is a set of two or more equations containing the same unknowns.

let’s take a look at systems of equations, and see what the graphs of individual equations within a system reveal about the mathematical relationship of the variables.

systems of equations

a system of equations contains two or more linear equations that share two or more unknowns. to find a solution for a system of equations, we must find a value (or range of values) that is true for all equations in the system.

the graphs of equations within a system can tell us how many solutions exist for that system. look at the images below. each show two lines that make up a system of equations (in the graph on the right the two lines are superimposed and look like a single line). how many points in common does each system of lines reveal?

one solution

no solutions

infinite solutions

if the graphs of the equations intersect, then there is one solution that is true for both equations.

if the graphs of the equations do not intersect (for example, if they are parallel), then there are no solutions that are true for both equations.

if the graphs of the equations are the same, then there are an infinite number of solutions that are true for both equations.

remember, the graph of a line represents every point that is a possible solution for the equation of that line. so when the graphs of two equations cross, the point of intersection lies on both lines, meaning that it is a possible solution for both equations. when the graphs of two equations never touch, there are no shared points and there are no possible solutions for the system. when the graphs of two equations lie on top of one another, they share all their points and every one is a possible solution.

graphing as a solution method

graphing equations in order to identify a specific point of intersection is usually not a precise way to solve systems because it is often difficult to see exactly where two lines intersect (unless you are using a computer-based graphing program that allows you to zoom in on a point). however, the graph of a system of equations can still give a good idea of what type of solution, if any, exists. let’s graph a system, and see how it works.

graph the system y = 3x and x + 2y = 4. how many solutions does this system have?

a graph of the two lines y = 3x and x + 2y = 4 shows us that the lines intersect, meaning that there is a single (x, y) value that satisfies both equations. looking at the graph does not tell us exactly where that point is, but we don’t need to know that information here, because the question only asks for the number of solutions.

so a system made of two intersecting lines has one solution. now let’s look at a different situation:

how many solutions exist for the system y -0.5x = 7 and 2y = x − 3?

plotting both equations, it looks like there is no solution—the lines are parallel. to check this finding, we can compare the slopes of the equations. to make that easy, we’ll rearrange the equations into slope-intercept form, or y = mx + b.   that gives us the equations y = 0.5x + 7 and y = 0.5x − 1.5.   yes, the slope of both lines is 0.5, which means the lines really are parallel. they never intersect, so there is no point that lies on both lines, and no solution to the system.

step-by-step explanation: