Page 121 - Maths Skills - 8

Comparing Quantities 119

Example 2: Sanjeev bought a shirt for ` 336 including 12% GST and a neck tie for ` 110, including 10% GST.
Find the list price of shirt and neck tie together. [Note: List price means marked price.]

100
Solution: List price of the shirt = ` × 336 = ` 300
112
100
List price of the neck tie = ` × 110 = ` 100
110
List price of both = ` 300 + ` 100 = ` 400.
Example 3: Sunil bought a TV for ` 22000 including GST of 10%. Find the price of the TV before GST was
added.
Solution: Inclusion of 10% GST means that if the original price is ` 100, then the price including GST
is ` 110.

Thus, when price including GST is ` 110, original price is ` 100.
100
⇒ When price including GST is ` 22,000 original price is ` × 22000 = ` 20,000.
110

Exercise 8.3

1. The cost of a pair of roller skater at a shop was ` 450. The GST charged was 5%. Find the bill amount.

2. The price of a TV is ` 13,000. The GST charged on it is at the rate of 12%. Find the amount that Vikas
will have to pay if he buys it.
3. Waheeda bought an air cooler for ` 3500, including GST of 10%. Find the price of the air cooler before
GST was added.
4. List price of a shirt is ` 870. If Vinay paid ` 87 as GST for it, find the rate of GST.

5. Shruti bought an iron for ` 2200 (including 10% GST). Find the price of the iron before the GST was
added.

6. Find the amount when 6% GST is added on the purchase of 6 kg sugar at the rate of ` 20 per kg.
7. A TV is available for ` 13,750 including GST. If the market price of the TV is ` 12,500, what is the rate
of GST?

COMPOUND INTEREST
In banks, post offices, insurance corporations, and other institutions which lend money and accept deposits, here
the interest is not calculated on the basis of simple interest. In such cases, the interest obtained during the first
time period is added to the original principal and the amount so obtained is the new principal for the second time
period and so on. The difference between the amount obtained at the last time period and the original principal is
called as the compound interest on the original principal for that time period.
Here, we will discuss about the calculation of compound interest on different conversion periods, i.e., the fixed
time period after which the interest is calculated and added to the principal to form the new principal for the next
time period.

(i) Calculation of Compound Interest When Interest is Compounded Annually

In such cases, the interest obtained during the first year is added to the original principal and the amount so
obtained is the new principal for the second year. The amount obtained at the end of second year becomes the
principal for the third year and so on.