Surya thought of a number, added 15 to it, then divided the sum by 2 and got 10 as his answer. The number Surya thought of was _________. [3 marks]

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Solution

Let the number Surya thought of = $x$ . [0.5 mark]
So the equation from the given statement = $\frac{(x + 15)}{2} = 10$ [1 mark]
$\Rightarrow (x + 15) = 10 \times 2$
$\Rightarrow (x + 15) = 20$ [0.5 mark]
$\Rightarrow x = 20 - 15$ [0.5 mark]
$\Rightarrow x = 5$ [0.5 mark]
So, the number that he thought of was 5.

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Surya thought of a number, added 15 to it, then divided the sum by 2 and got 10 as his answer. The number Surya thought of was _________. [3 marks]

Let the number Surya thought of = x. [0.5 mark] So the equation from the given statement = (x+15)2=10 [1 mark] ⇒(x+15)=10×2 ⇒(x+15)=20 [0.5 mark] ⇒x=20−15 [0.5 mark] ⇒x=5 [0.5 mark] So, the number that he thought of was 5.