Divisibility Problem- AMC 8 (2016) - Question 5

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What are we learning ?

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Competency in Focus: Divisibility.

This problem from American Mathematics contest (AMC 8, 2016) is based on the concept of divisibility .

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First look at the knowledge graph.

[/et_pb_text][et_pb_image src="https://cheenta.com/wp-content/uploads/2020/02/amc8_2016_5.png" align="center" force_fullwidth="on" _builder_version="4.2.2" min_height="388px" height="198px" max_height="207px"][/et_pb_image][et_pb_text _builder_version="4.2.2" text_font="Raleway|300|||||||" text_text_color="#ffffff" header_font="Raleway|300|||||||" header_text_color="#e2e2e2" header_2_font="Aclonica||||||||" background_color="#0c71c3" custom_padding="20px|20px|20px|20px" border_radii="on|5px|5px|5px|5px" box_shadow_style="preset3" inline_fonts="Aclonica"]

Next understand the problem

[/et_pb_text][et_pb_text _builder_version="4.2.2" text_font="Raleway||||||||" text_font_size="20px" text_letter_spacing="1px" text_line_height="1.5em" background_color="#f4f4f4" custom_margin="10px||10px" custom_padding="10px|20px|10px|20px" box_shadow_style="preset2"]The number $N$ is a two-digit number.• When $N$ is divided by $9$, the remainder is $1$.• When $N$ is divided by $10$, the remainder is $3$.What is the remainder when $N$ is divided by $11$? $\textbf{(A) }0\qquad\textbf{(B) }2\qquad\textbf{(C) }4\qquad\textbf{(D) }5\qquad \textbf{(E) }7$[/et_pb_text][/et_pb_column][/et_pb_row][et_pb_row _builder_version="4.0"][et_pb_column type="4_4" _builder_version="3.25" custom_padding="|||" custom_padding__hover="|||"][et_pb_accordion open_toggle_text_color="#0c71c3" _builder_version="4.2.2" toggle_font="||||||||" body_font="Raleway||||||||" text_orientation="center" custom_margin="10px||10px" hover_enabled="0"][et_pb_accordion_item title="Source of the problem" _builder_version="4.2.2" open="off"]American Mathematical Contest 2016, AMC 8  Problem 5[/et_pb_accordion_item][et_pb_accordion_item title="Key Competency" _builder_version="4.2.2" hover_enabled="0" open="off"]

Divisibility

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Start with hints 

[/et_pb_text][et_pb_tabs _builder_version="4.2.2"][et_pb_tab title="HINT 0" _builder_version="4.0.9"]Do you really need a hint? Try it first![/et_pb_tab][et_pb_tab title="HINT 1" _builder_version="4.2.2"]When $N$ is divided by $10$ it leaves remainder $3$i.e., $N=10\times P+3 \textbf{ ,where } P$ is an integer.i.e., The unit digit of $N$ must be $3$ because unit digit of $10P$ is zero.[/et_pb_tab][et_pb_tab title="HINT 2" _builder_version="4.2.2"]$N$ leaves remainder $1$ when divided by $9$.i.e., $N=9\times Q+1$ where $Q$ is an integer.Since $10\times P+3=9\times Q+1$the unit digit of $9\times Q +1 $ must be $3$.    [/et_pb_tab][et_pb_tab title="HINT 3" _builder_version="4.2.2"]Since $N$ is a two digit number then the only possibility is $Q=8$i.e., $N=9\times 8+1=73$[/et_pb_tab][/et_pb_tabs][/et_pb_column][/et_pb_row][/et_pb_section][et_pb_section fb_built="1" fullwidth="on" _builder_version="4.2.2" global_module="50833"][et_pb_fullwidth_header title="AMC - AIME Program" button_one_text="Learn More" button_one_url="https://cheenta.com/amc-aime-usamo-math-olympiad-program/" header_image_url="https://cheenta.com/wp-content/uploads/2018/03/matholympiad.png" _builder_version="4.2.2" title_level="h2" background_color="#00457a" custom_button_one="on" button_one_text_color="#44580e" button_one_bg_color="#ffffff" button_one_border_color="#ffffff" button_one_border_radius="5px"]

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