NCERT Exemplar Solutions
Class 7 - Mathematics - Unit 4: Simple Equations - Problems and Solutions
Question 105

Question. 105

What does a duck do when it flies upside down? The answer to this riddle is hidden in the equation given below:

If i + 69 = 70, then i = ?

If 8u = 6u + 8, then u = ?

If 4a = −5a + 45, then a = ?

If 4q + 5 = 17, then q = ?

If −5t − 60 = −70, then t = ?

If (1/4)s + 98 = 100, then s = ?

If (5/3)p + 9 = 24, then p = ?

If 3c = c + 12, then c = ?

If 3(k + 1) = 24, then k = ?

For riddle answer: substitute the number for the letter it equals.

Answer:

i = 1, u = 4, a = 5, q = 3, t = 2, s = 8, p = 9, c = 6, k = 7

Detailed Answer with Explanation:

Solving each equation:

  • i + 69 = 70 ⇒ i = 1
  • 8u = 6u + 8 ⇒ 2u = 8 ⇒ u = 4
  • 4a = −5a + 45 ⇒ 9a = 45 ⇒ a = 5
  • 4q + 5 = 17 ⇒ 4q = 12 ⇒ q = 3
  • −5t − 60 = −70 ⇒ −5t = −10 ⇒ t = 2
  • (1/4)s + 98 = 100 ⇒ (1/4)s = 2 ⇒ s = 8
  • (5/3)p + 9 = 24 ⇒ (5/3)p = 15 ⇒ p = 9
  • 3c = c + 12 ⇒ 2c = 12 ⇒ c = 6
  • 3(k + 1) = 24 ⇒ k + 1 = 8 ⇒ k = 7
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