{"id":"cb_question_bank:12b4e8a6-e7d5-4acc-9336-0f87f6f44eb1","source_id":"cb_question_bank","source_item_id":"12b4e8a6-e7d5-4acc-9336-0f87f6f44eb1","external_id":null,"ibn":"11189-DC","question_id":"371cbf6b","program":"SAT","module":"math","domain_code":"P","domain":"Advanced Math","skill_code":"P.A.","skill":"Equivalent expressions","difficulty":"H","score_band":6,"answer_type":"mcq","answer_source":"key","layout_warning":null,"form_id":null,"module_number":null,"position":null,"stem":"The equation above is true for all x , where a and b are constants. What is the value of ab ?","stimulus":"open parenthesis, a x plus 3, close parenthesis, times, open parenthesis, 5 x squared, minus b x, plus 4, close parenthesis, equals, 20 x cubed, minus 9 x squared, minus 2 x, plus 12","stimulus_html":"<div class=\"stimulus_reference \">\n        <p class=\"standalone_statement style:1 \">\n          <span class=\"math_expression \">\n            <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/2617c9cac2c0f0d3744d7a1f2e16cafdcf786cc3373769799820fb81c054339a\" alt=\"open parenthesis, a x plus 3, close parenthesis, times, open parenthesis, 5 x squared, minus b x, plus 4, close parenthesis, equals, 20 x cubed, minus 9 x squared, minus 2 x, plus 12\"></span></span>\n        </p>\n      </div>\n","stem_html":"<p class=\"stem_paragraph \">The equation above is true for all <span class=\"italic\">x</span>, where <span class=\"italic\">a</span> and <span class=\"italic\">b</span> are constants. What is the value of <span class=\"italic\">ab</span> ?</p>\n","rationale_html":"<p>Choice C is correct. If the equation is true for all <span class=\"italic\">x</span>, then the expressions on both sides of the equation will be equivalent. Multiplying the polynomials on the left-hand side of the equation gives <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/3aed2bb52ab5a8ea7664a5ce824ee211901853219583103d400bd039432225bf\" alt=\"5 a, x cubed, minus a, b x squared, plus 4 a, x, plus 15 x squared, minus 3 b x, plus 12\"></span>. On the right-hand side of the equation, the only <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/3a186314172bc239fb025135d8722d39ee39bfefe4e212836956158aa0b9ff08\" alt=\"x squared\"></span>-term is <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/ba803fa888fbfb328f362ec53686df3f9ac0197c1d46e2ff2061ae0b333f1d06\" alt=\"negative 9 x squared\"></span>. Since the expressions on both sides of the equation are equivalent, it follows that <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/05480c0e38092377d001696cd2ac4fc757658532570704632e4e4149b8e27b8b\" alt=\"negative a, b x squared, plus 15 x squared, equals negative 9 x squared\"></span>, which can be rewritten as <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/9a7edeedd80f42bd41ad4d1fbdcabecaf9eb536624f784889d599ca7fb486c07\" alt=\"open parenthesis, negative a, b plus 15, close parenthesis, times x squared, equals negative 9 x squared\"></span>. Therefore, <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/43bba863a2f35395ece354135dabb16c991ab243fb78267dbc2c1d33a37be0ad\" alt=\"negative a, b plus 15, equals negative 9\"></span>, which gives <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/4a20dd662a837cf35008a5b1d0198c71785e0d418ecb6af7c18b4d41f5f3efff\" alt=\"a, b equals 24\"></span>.</p><p>Choice A is incorrect. If <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/6d5757d03567ec54294b517eb90610515e5bdeffbfabbd6a31988d79991c4862\" alt=\"a, b equals 18\"></span>, then the coefficient of <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/3a186314172bc239fb025135d8722d39ee39bfefe4e212836956158aa0b9ff08\" alt=\"x squared\"></span> on the left-hand side of the equation would be <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/4c0a55fcb0e7d2b310c213fae04ea529a4574ae32779136b1f2fbfcc1412c6f2\" alt=\"negative 18 plus 15, equals negative 3\"></span>, which doesn’t equal the coefficient of <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/3a186314172bc239fb025135d8722d39ee39bfefe4e212836956158aa0b9ff08\" alt=\"x squared\"></span>, <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/85427db1337a88f32c150849afd30d75356f31a9f7c40b1e77f5872ce3416796\" alt=\"negative 9\"></span>, on the right-hand side. Choice B is incorrect. If <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/75780594a838349d104e4cac1f5ff4f8e77431c2ed718cd6071e3afe16cd2f90\" alt=\"a, b equals 20\"></span>, then the coefficient of <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/3a186314172bc239fb025135d8722d39ee39bfefe4e212836956158aa0b9ff08\" alt=\"x squared\"></span> on the left-hand side of the equation would be <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/86e6dadf4460913293f9aa18cf283423599c5e1824870eace0c62a14aa73555d\" alt=\"negative 20 plus 15, equals negative 5\"></span>, which doesn’t equal the coefficient of <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/3a186314172bc239fb025135d8722d39ee39bfefe4e212836956158aa0b9ff08\" alt=\"x squared\"></span>, <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/85427db1337a88f32c150849afd30d75356f31a9f7c40b1e77f5872ce3416796\" alt=\"negative 9\"></span>, on the right-hand side. Choice D is incorrect. If <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/7f820c76ec6fa4c1a9ef5591f02f4594ee9f604902675b77447cae571afebe6e\" alt=\"a, b equals 40\"></span>, then the coefficient of <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/3a186314172bc239fb025135d8722d39ee39bfefe4e212836956158aa0b9ff08\" alt=\"x squared\"></span> on the left-hand side of the equation would be <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/0fe8716023d416a0ddaa22e19fad9e7a82834a1f57b800b4541cf6385d08e41d\" alt=\"negative 40 plus 15, equals negative 25\"></span>, which doesn’t equal the coefficient of <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/3a186314172bc239fb025135d8722d39ee39bfefe4e212836956158aa0b9ff08\" alt=\"x squared\"></span>, <span class=\"math-container\"><img align=\"middle\" role=\"math\" class=\"math-img\" src=\"/api/assets/85427db1337a88f32c150849afd30d75356f31a9f7c40b1e77f5872ce3416796\" alt=\"negative 9\"></span>, on the right-hand side.</p><p></p>\n","correct_answer":["C"],"has_media":true,"has_mathml":false,"has_table":false,"source_created_at":"2023-08-02T20:25:59.638000+00:00","source_updated_at":"2023-08-02T20:25:59.638000+00:00","options":[{"label":"A","content_html":"<p class=\"choice_paragraph \">18</p>\n","ord":0},{"label":"B","content_html":"<p class=\"choice_paragraph \">20</p>\n","ord":1},{"label":"C","content_html":"<p class=\"choice_paragraph \">24</p>\n","ord":2},{"label":"D","content_html":"<p class=\"choice_paragraph \">40</p>\n","ord":3}],"attribution":{"source_id":"cb_question_bank","source_name":"College Board digital SAT question bank (community dump)","rights_holder":"College Board","canonical_url":"https://satsuitequestionbank.collegeboard.org/","retrieved_from":"https://raw.githubusercontent.com/mdn522/sat-question-bank/main/data/cb-digital-questions.json","attribution":"SAT practice questions © College Board, from the official SAT Suite Question Bank. Retrieved via the community dump at github.com/mdn522/sat-question-bank.","disclaimer":"SAT® and PSAT/NMSQT® are trademarks registered by the College Board, which is not affiliated with, does not sponsor, and does not endorse this project.","license":"College Board copyright; source repository carries no licence. Local use only.","redistributable":false,"item_count":2017}}