Mary, who is sixteen years old, is four times as old as her brother. how old will mary be when she is twice as old as her brother? explained

First, you find the brother's age by dividing mary's age by 4.
16 ÷ 4 = 4
Now that you have two ages, you can just make a list to find the answer.
16 and 4
18 and 6
20 and 8
22 and 10
24 and 12

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since the cosine is the ratio of the adjacent side to the hypotenuse, you can see that cos 60° = ½. answer. according to the property of cofunctions (topic 3), sin 30° is equal to cos 60°. sin 30° = ½.