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If a - b = 3 and \begin{aligned} a^2 + b^2 = 29 \end{aligned}, then find the value of ab

  • 7
  • 8.5
  • 10
  • 12

Answer: Option C

Explanation:

Remember the formula, if not then cram it :)
\begin{aligned} 2ab = (a^2 + b^2)- (a-b)^2 \end{aligned}
=> 2ab = 29 - 9 = 20
=> ab = 10

Similar Questions :

1. Value of \begin{aligned} 2^5 \times 9^2 \end{aligned} has been written as 2596, what is the difference between actual value.

  • 1
  • 2
  • 3
  • 4

Answer: Option D

2. In a class free notebooks were distributed among all the children. Each child got notebooks which were one-eighth of the number of children. If number of children been half, then each child would have recieved 16 notebooks in total. Find the total number of books distributed.

  • 450
  • 512
  • 598
  • 658

Answer: Option B

Explanation:

Let suppose total number of students in class are X.
Then from the question we can conclude it that,
\begin{aligned}
X*\frac{1}{8}X = \frac{X}{2}*16 \\
=> X = 64\\
\text{Total notebooks,} \\
= \frac{1}{8}X^2 \\
= \left( \frac{1}{8} * 64 * 64 \right) \\
= 512
\end{aligned}

3. 5.8 * 2.5 + 0.6 * 6.75 + 139.25= ?

  • 157.60
  • 147.80
  • 147.60
  • 157.80

Answer: Option D

4. 3034 - (1002 / 20.04) = ?

  • 2984
  • 2983
  • 2982
  • 2981

Answer: Option A

5. If p - q = 3 and
\begin{aligned} p^2 + q^2 = 29 \end{aligned}, find the value of pq.

  • 7
  • 8
  • 9
  • 10

Answer: Option D

Explanation:

We know
\begin{aligned} 2ab = (a^2 + b^2) - (a - b)^2 \end{aligned}

\begin{aligned} 2pq = 29 - 9 = 20 \end{aligned}

\begin{aligned} =>pq = 10 \end{aligned}

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