Discussion
If a number is first decreased by 10 % and then increased by 10 %. The number so obtained is 70 less than the original number. The original number is
Answer: C
The original number is 7000.
A 10% decrease followed by a 10% increase multiplies the number by \(0.9 \times 1.1 = 0.99\), a net loss of 1%:
\[ x - 0.99x = 0.01x = 70 \Rightarrow x = 7000 \]
Check: 7000 falls to 6300, then rises to 6930, which is 70 less than 7000. 700 would give a fall of only 7. The common mistake is to assume the decrease and increase cancel; they do not, because the 10% rise is taken on the smaller number.
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