Algebraic expressions

Correct answer: A. -30

Explanation: Substituting m=3 and n=-2, m²n=3²×(-2)=9×(-2)=-18, while mn²=3×(-2)²=3×4=12. Therefore, m²n-mn²=-18-12=-30. Option -6 is not correct because it does not correctly subtract the second term, 12. Exam tip: the square of a negative number is positive, so (-2)²=4.

Correct answer: A. \(3x+6\)

Explanation: First simplify the innermost grouping: \(3x-\{x-4\}=3x-x+4=2x+4\). Then \(5(x+2)-[2x+4]=5x+10-2x-4=3x+6\). Therefore, the correct option is \(3x+6\). The result \(3x+14\) can occur if the minus sign before the bracket is not distributed correctly. Exam tip: when removing a bracket preceded by a minus sign, change the signs of all terms inside it.

Correct answer: A. \(2x-1\)

Explanation: The number 2 more than \(x\) is \(x+2\), and the number 3 less than \(x\) is \(x-3\). Therefore, their sum is \((x+2)+(x-3)=2x-1\). The expression \(2x+5\) would result from adding 3 instead of subtracting it. Exam tip: translate “more than” as addition and “less than” as subtraction before simplifying.

Correct answer: A. (\frac{x}{2})

Explanation: (\frac{x}{3}=\frac{2x}{6}), so (\frac{5x}{6}-\frac{2x}{6}=\frac{x}{2}). Make common denominators for fraction terms.

Correct answer: A. 13

Explanation: Given \(x+y=5\) and \(x-y=1\), substitute these values directly: \(2(x+y)+3(x-y)=2\times5+3\times1=10+3=13\). Therefore, 13 is correct. The value 11 does not result from correct substitution. Exam tip: When \(x+y\) and \(x-y\) are given directly, there is no need to find \(x\) and \(y\) separately.

Correct answer: A. (3x^2+5xy+y^2)

Explanation: The direct answer is option A: \(3x^2+5xy+y^2\). To simplify an algebraic expression, combine only like terms. Like terms have the same variables with the same powers. First combine the \(x^2\) terms: \(6x^2-3x^2=3x^2\). Next combine the \(xy\) terms: \(-4xy+9xy=5xy\). Finally combine the \(y^2\) terms: \(2y^2-y^2=y^2\). Therefore the result is \(3x^2+5xy+y^2\). Option A is correct because it contains all three correctly combined terms. Option B has \(9x^2\), but the coefficient should be 3. Option C has \(-13xy\), but \(-4+9=5\), not -13. Option D gives incorrect coefficients for several terms. Remember: collect identical variable parts separately; never combine \(x^2\), \(xy\), and \(y^2\) as though they were the same.

Correct answer: A. 34

Explanation: Substituting t=2 gives 3(2^4)-2(2^3)+2. Since 2^4=16 and 2^3=8, the value is 3×16-2×8+2=48-16+2=34. The value 36 may result from incorrectly omitting the final +t term. Exam tip: evaluate powers first, then perform multiplication and addition/subtraction.

Correct answer: A. (3(a-b)+(a+b))

Explanation: The difference is (a-b), and three times it is (3(a-b)). Adding the sum (a+b) gives (3(a-b)+(a+b)).

Correct answer: A. \(5x-9\)

Explanation: A minus sign occurs before the last bracket, so the signs of both terms inside it must change: \((2x+3)+(4x-7)-(x+5)=2x+3+4x-7-x-5\). Combining like terms gives \((2x+4x-x)=5x\) and \((3-7-5)=-9\). Therefore, the simplified form is \(5x-9\). The option \(5x+1\) results from handling the constant \(-5\) incorrectly. Exam tip: whenever a bracket is preceded by a minus sign, reverse the sign of every term inside it.

Correct answer: A. The claim is correct; it has three terms and the highest exponent is 2.

Explanation: \(7x^2\), \(-3x\), and \(5\) are three separate terms, so the expression is a trinomial. For degree, take the greatest exponent of the variable: \(x^2\) has exponent 2. The coefficient 3 in \(-3x\) is not the degree. Exam tip: count terms and find degree separately.

Correct answer: A. \(3x-7y\)

Explanation: The subtraction is \((4x-2y)-(x+5y)\). The minus sign before the second bracket changes the signs of both its terms: \(4x-2y-x-5y\). Combining like terms gives \(4x-x=3x\) and \(-2y-5y=-7y\), so the result is \(3x-7y\). In \(5x-7y\), the \(x\)-terms have been incorrectly added. Exam tip: when a bracket is preceded by a minus sign, change the sign of every term inside it.

Correct answer: A. \(10x^2y-7xy^2\)

Explanation: \(3x^2y\) and \(7x^2y\) are like terms, so adding their coefficients gives \(10x^2y\). Similarly, \(-5xy^2\) and \(-2xy^2\) combine to give \(-7xy^2\). Therefore, the simplified expression is \(10x^2y-7xy^2\). Option B incorrectly treats the negative second terms as positive. Exam tip: combine only those terms that have the same variables raised to the same powers.

Correct answer: A. 8

Explanation: On substituting \(q=3\), we get \(q^3=3^3=27\). Hence, \(\frac{q^3-q}{3}=\frac{27-3}{3}=\frac{24}{3}=8\). Therefore, option A is correct. The value 6 can result from an error in evaluating the exponent or simplifying the numerator. Exam tip: evaluate powers first, then simplify the numerator before dividing.

Correct answer: A. \(4n+6\)

Explanation: The four consecutive integers are \(n, n+1, n+2\), and \(n+3\). Their sum is \(n+(n+1)+(n+2)+(n+3)=4n+6\), so option A is correct. In \(4n+4\), the extra parts of the consecutive integers, \(1+2+3=6\), have not been added correctly. Exam tip: Write consecutive integers by adding \(1,2,3\), and so on, to the first integer.

Correct answer: A. \(3x-6\)

Explanation: First simplify the square bracket: \(x-2(1-x)=x-2+2x=3x-2\). Also, \(2(3x-4)=6x-8\). Therefore, the expression becomes \(6x-8-(3x-2)=6x-8-3x+2=3x-6\). Hence, option A is correct. The result \(3x-10\) can arise if the sign of \(+2\) is handled incorrectly while subtracting \((3x-2)\). Exam tip: when a minus sign occurs before a bracket, change the sign of every term inside it.

Correct answer: A. 12

Explanation: Substituting the given values, x+y=2+1=3. Therefore, 2(x+y)^2-3xy=2(3)^2-3(2)(1)=2×9-6=18-6=12. Hence, the correct answer is 12. The value 18 is only the first term, 2(x+y)^2; the term 3xy must also be subtracted. Exam tip: evaluate brackets first, then powers and multiplication, and finally addition or subtraction.

Correct answer: A. 12

Explanation: On substituting the given values, x+y=2+1=3 and xy=2×1=2. Therefore, 2(x+y)^2-3xy=2(3)^2-3(2)=2×9-6=12. Option C, 18, is only the value of 2(3)^2; it does not subtract 3xy. Exam tip: evaluate brackets and powers before carrying out multiplication and subtraction.

Correct answer: A. \(3a+4b\)

Explanation: Combine like terms in the expression: \(2a+5a-4a=3a\) and \(-3b+7b=4b\). Hence, the simplified form is \(3a+4b\). In \(11a+4b\), the negative sign of \(-4a\) has been ignored while combining the \(a\)-terms. Exam tip: add or subtract only terms having the same variable and exponent.

Correct answer: A. \(10x+6\)

Explanation: The perimeter of a rectangle is \(2(\text{length}+\text{breadth})\). Thus, \(2[(3x-2)+(2x+5)]=2(5x+3)=10x+6\). Hence, the correct expression is \(10x+6\). The expression \(5x+3\) is only the sum of the length and breadth, not the perimeter. Exam tip: A perimeter includes all four sides, so multiply the sum of length and breadth by 2.

Correct answer: A. -4

Explanation: Substitute x=1. Since \(1^3=1\) and \(1^2=1\), \(4(1)^3-6(1)^2+5(1)-7=4-6+5-7=-4\). Therefore, -4 is correct. The nearby distractor -3 can result from an error in addition or subtraction. Exam tip: after substitution, write the sign of every term before simplifying.

Correct answer: A. x + 8

Explanation: First simplify the innermost bracket: 3x - (x + 4) = 3x - x - 4 = 2x - 4. Then, 5x - 2(2x - 4) = 5x - 4x + 8 = x + 8. Hence, x + 8 is correct. The option x - 8 results from handling the sign incorrectly when multiplying 2 by -4. Exam tip: When a bracket is preceded by a minus sign or a multiplier, apply it to every term inside the bracket.

Correct answer: A. \(2x^2-6x+12\)

Explanation: To subtract the second expression, change the sign of each of its terms: \((3x^2-2x+7)-(x^2+4x-5)=3x^2-2x+7-x^2-4x+5\). Combining like terms gives \(2x^2-6x+12\), so option A is correct. In option B, the \(4x\) term has effectively been added instead of subtracted. Exam tip: When a minus sign precedes brackets, change the signs of all terms inside the brackets.

Correct answer: A. \(2x-41\)

Explanation: First expand the brackets: \(7(2x-3)=14x-21\) and \(-4(3x+5)=-12x-20\). Combining like terms gives \(14x-12x-21-20=2x-41\). Therefore, the correct answer is \(2x-41\). In \(2x-1\), the constant terms have been combined incorrectly. Exam tip: When a negative multiplier is before a bracket, apply it to every term inside the bracket.

Correct answer: B. 33

Explanation: Substituting x=-4 gives 3x^2+2x-7=3(-4)^2+2(-4)-7. Since (-4)^2=16, we get 3×16-8-7=48-15=33. Therefore, 33 is correct. A value such as 49 can result from a sign error while handling 2x and 7. Exam tip: always write a negative value in brackets before squaring it.

Correct answer: C. (5a^2+7a+3)

Explanation: Combining like terms gives (9a^2-4a^2=5a^2), (-6a+13a=7a), and (11-8=3). Group terms by powers.