Exercise: 7-E
Mental Maths
Q1: Fill in the blanks:
i. _______ =\(\frac{\left(100+gain%\right)}{100}\times\) _______.
Answer: S.P. = \(\frac{(100 + \text{gain} \%)}{100} \times\) C.P.
ii. Discount is always allowed on the ________ price.
Answer: Marked
iii. ________ = M.P. – Discount.
Answer: Selling Price
iv. If the S.P of an article is \(\frac{6}{5}\) of its cost price, then the gain per cent is _______.
\[
\text{Gain\%} = \left(\frac{6}{5} – 1\right) \times 100 = \frac{1}{5} \times 100 = 20\%
\]
Answer: 20%
v. A shopkeeper incurs a _______ if he sells 15 articles at the cost price of 12 articles.
Let C.P. of 1 article = ₹1 ⇒ C.P. of 15 articles = ₹15
If he sells 15 articles at C.P. of 12 articles ⇒ S.P. = ₹12
Loss = ₹3 on ₹15 ⇒ Loss% = \(\frac{3}{15} \times 100 = 20\%\)
Answer: loss of 20%
Q2: Write true (T) or false (F):
i. Gain or loss is always reckoned on the S.P.
Answer: False (F)
Explanation: Gain or loss is always calculated on the Cost Price (C.P.), not the Selling Price (S.P.)
ii. If a shopkeeper buys an article for ₹75 and sells it for ₹100, then his gain is 25%.
Gain = ₹100 − ₹75 = ₹25
Gain% = \(\frac{25}{75} \times 100 = 33\frac{1}{3}\%\)
Answer: False (F)
iii. C.P. = \(\frac{100}{\left(100-loss%\right)}\times\) S.P.
Answer: True (T)
Explanation: This is the correct formula to find C.P. when loss% and S.P. are known.
iv. If no discount is given, then cost price becomes equal to selling price.
Answer: False (F)
Explanation: If no discount is given, the marked price equals the selling price, not necessarily the cost price.





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