A box contains 14 crayons. 11 crayons are purple (P) and 3 crayons are brown (B). You remove one crayon and put it back into the box. Then, you take out another crayon.

Construct a tree diagram depicting all possible outcomes of the above event and answer the question that follows.

What is the probability of choosing at least one brown crayon?

INSTRUCTION: Give your answer as a simplified fraction.

<p>In this tutorial, we will learn about the <a data-lesson="history-of-life" data-subject="biology" data-tutorial="evolution-overview" href="https://app.ulearngo.com/biology/evolution-overview/history-of-life">history of life</a> on Earth. We will first talk about tools (fossil dating) and theories, (continental drift) that help us understand our past. Next we will look at the geological time-scale and discuss three major eras: the Paleozoic, Mesozoic and Cenozoic. We will talk about the Cambrian explosion, which was a major explosion in the diversity of life, and we will discuss mass extinctions, which were mass losses in the <a href="https://app.ulearngo.com/tutorials/introducing-study-of-life/diversity-of-life">diversity of life</a> forms. We will also look at the evolution of humans in the last 4 million years. Throughout the topic will look at fossil evidence from Africa that originates from key periods in Earth's history.</p>
<div class="note keyconcepts">
<ul>
<li>Scientists use <a href="https://app.ulearngo.com/tutorials/introducing-study-of-life/scientific-reasoning">deductive reasoning</a> to understand <a data-lesson="fossils" data-subject="biology" data-tutorial="evolution-overview" href="https://app.ulearngo.com/biology/evolution-overview/fossils">fossils</a> and the history of life on Earth.</li>
<li>Geological events often caused changes in climate, which in turn influence the emergence and disappearance of species.</li>
<li>It takes special circumstances for fossils to form, and fossils can be dated by radiometric, radiocarbon or relative dating.</li>
<li>Climate and geography helped shape the <a data-lesson="evolution-of-life" data-subject="biology" data-tutorial="biology-foundations" href="https://app.ulearngo.com/biology/biology-foundations/evolution-of-life">evolution of life</a> on Earth.</li>
<li>Geological timescales are divided into eons, eras and periods.</li>
<li>The Cambrian explosion was a rapid explosion in the diversity of life-forms. All animal groups have their origin in the Cambrian explosion.</li>
<li>Mass extinctions are massive losses in life, and there have been five <a data-lesson="mass-extinction" data-subject="biology" data-tutorial="ecology-overview" href="https://app.ulearngo.com/biology/ecology-overview/mass-extinction">mass extinction</a> events in history.</li>
<li>In the last 4 million years significant changes have occurred in <a data-lesson="summarizing-community-ecology" data-subject="biology" data-tutorial="population-community-ecology" href="https://app.ulearngo.com/biology/population-community-ecology/summarizing-community-ecology">species</a> occurring in Africa, including the evolution of humans.</li>
<li>Humans have a massive effect on <a data-lesson="biodiversity" data-subject="biology" data-tutorial="ecology-overview" href="https://app.ulearngo.com/biology/ecology-overview/biodiversity">biodiversity</a> and the natural environment and are partially responsible for the '6th mass extinction'.</li>
<li>Africa is rich in many fossils from diverse time periods.</li>
<li>Fossil tourism is a source of income and employment in fossil localities.</li>
</ul>
</div>
<p><img src="https://data.ulearngo.com/assets/0fa528ec-65bf-4332-90c0-98fc952d6d29"/></p>

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History of Life on Earth

Biology studies life and living organisms. Biology can be divided into different sections that cover the morphology, physiology, anatomy, behavior, and so on of living organisms.

Biology

Explore the evolution of life on Earth through geological timescales, continental drifts, natural selection, and methods of dating fossils, and gain insights into the causes and impacts of past and ongoing mass extinctions.


History of Life on Earth

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