Find the missing number.
$120, 80, 40, 45, ?, 5$

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Solution

Find the missing number.
The given series is, $120, 80, 40, 45, ?, 5$
It is observed that the given series is the combination of two different series $120, 80, 40 and 45, ?, 5$ .
The first series $120, 80, 40$ are in AP where the common difference is $- 40$ .
As we know, the difference between two consecutive terms of arithmetic progression always remains the same.
Let the unknown number is $x$
$∴ x - 45 = 5 - x \Rightarrow x + x = 5 + 45 \Rightarrow 2 x = 50 \Rightarrow x = \frac{50}{2} \Rightarrow x = 25$
Hence, the missing number is $25$ .

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Find the missing number.120,80,40,45,?,5

Find the missing number.
$120, 80, 40, 45, ?, 5$