Variance Of Binomial Distribution – Formula, Definition With Examples

Here at Brighterly, we believe in making complex mathematical concepts digestible and fun for children. Diving into the world of probability might seem daunting initially, but understanding its elements can open up a realm of exciting possibilities. One such pivotal concept is the binomial distribution, and a key component within that is the variance of the binomial distribution. This article is designed to walk young learners and curious minds through the intricate yet fascinating landscape of binomial distribution and its variance. So, let’s embark on this mathematical adventure together!

What Is the Binomial Distribution?

Binomial distribution, a cornerstone concept in the realm of probability theory, comes into play when you have a fixed number of trials, each with a constant probability of success. Imagine flipping a coin. If you’re curious about the number of times it lands heads up in, say, 10 flips, you’re delving into binomial distribution territory. This distribution is a discrete probability distribution, which means that the possible outcomes are countable, not continuous.

Definition of Binomial Distribution

At its core, the binomial distribution represents the probability of obtaining a certain number of successes in a specific number of trials. These trials should be independent of each other, and the outcome should be either a success or a failure. Such an event is often called a Bernoulli trial. For children to grasp, think of it like choosing between chocolate and vanilla – there are only two flavors (or outcomes) to pick from.

Definition of Variance in a Binomial Distribution

Variance quantifies the dispersion or spread of a set of data points. In the context of the binomial distribution, variance measures how spread out the number of successes might be from the expected value or mean. High variance indicates a larger spread, while low variance suggests outcomes are closer to the expected number of successes.

Properties of Binomial Distribution

The binomial distribution has some fascinating properties:

  • Fixed Number of Trials: There are a specific number of trials, which doesn’t change.
  • Two Possible Outcomes: Each trial results in just two possible outcomes, success or failure.
  • Constant Probability: The probability of success remains consistent throughout all the trials.
  • Independent Trials: One trial’s outcome doesn’t influence another.

Properties of Variance in Binomial Distribution

The variance in a binomial distribution also has distinct properties:

  • Depends on Two Factors: The variance depends on the number of trials (n) and the probability of success (p).
  • Larger for Intermediate p: The variance is largest when p is around 0.5 since outcomes are most unpredictable.

Difference Between Mean and Variance in Binomial Distribution

While both are measures of central tendency, the mean represents the average expected outcome, and variance illustrates the dispersion from this mean. In simpler terms, if the binomial distribution were a target, the mean would be the bullseye while the variance indicates how far the arrows (or outcomes) stray from the bullseye.

Formula for the Variance of a Binomial Distribution

The formula for the variance of a binomial distribution is given by:


  • is the number of trials.
  • is the probability of success on any given trial.

Understanding the Formula for Variance of Binomial Distribution

Let’s decode this formula. The term calculates the variance for one trial. Since we’re multiplying it by , the number of trials, it adjusts this single trial variance to reflect the variance across all the trials. Essentially, it accounts for the unpredictability of each event and scales it to the total number of events.

Writing Equations for Variance in Binomial Distribution

When dealing with the binomial distribution, the formula for variance, as we’ve discussed, is:

Always remember to plug in known values to solve for the unknowns.

Practice Problems on Variance of Binomial Distribution

1. If you flip a coin 20 times, and the probability of getting heads is 0.5, what’s the variance?


Plugging these values into our formula:

So, if you flip a coin 20 times, the variance in the number of heads you can expect is 5.

2. For a dice rolled 15 times, with the chance of getting a 6 being 1/6, calculate the variance.


Plugging these values into our formula:

Thus, when rolling a die 15 times, the variance in the number of times you can expect to roll a 6 is approximately 2.08.


Navigating through the nuances of probability theory, especially concepts like binomial distribution, might seem like scaling a tall mathematical mountain. But with each step, as with our guide on variance in the binomial distribution, we hope to make the ascent smoother and more enlightening. At Brighterly, we’re dedicated to illuminating the path of learning, making every mathematical journey a brighter and more enjoyable one. Whether you’re a student, teacher, parent, or just someone intrigued by the wonders of math, we hope this guide has brought you closer to mastering the world of binomial distributions. Let’s keep exploring, discovering, and learning together!

Frequently Asked Questions on Variance of Binomial Distribution

What is the significance of variance in binomial distribution?

The variance in a binomial distribution plays a crucial role as it quantifies how spread out or dispersed the outcomes of a binomial experiment are. This means that it gives us insights into the consistency or variability of results. For example, a higher variance might suggest that the outcomes can vary significantly from the average, while a lower variance indicates more consistent results close to the average.

Can variance be negative?

No, variance cannot be negative. This is because variance is a measure of the squared deviations from the mean. Since squaring any number (positive or negative) results in a positive value, the variance, being an average of these squared deviations, will always be non-negative. In simpler terms, it’s a measure of “distance” in a way, and distance can’t be negative.

How does the formula for variance relate to real-world scenarios?

The formula for variance in binomial distribution, , can be applied to many real-world scenarios where there are a fixed number of attempts and each attempt has a constant probability of success. For instance, in quality control, if a factory produces items and there’s a consistent probability that an item is defective, the formula can help estimate the spread of defects in a given sample size.

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