Question

Look up the rate list to see today's rates. Help Kiran to find out the cost of the junk.
• How much will Kiran pay for 31 kg newspaper?
1 kg newspaper costs Rs 5. 30 kg cost Rs 5 × 30 = Rs 150. So for 31 kg she pays Rs _____.
• How much will Kiran pay for 42 kg newspaper?
• Also find the cost of:
(a) 22 kg of plastic
(b) 23 kg of waste paper
(c) 12 kg of iron

Rate-List
Kind of Junk	Price of 1 Kg
1. Waste Paper	Rs 4/-
2. Newspaper	Rs 5/-
3. Iron	Rs 12/-
4. Brass	Rs 170/-
5. Plastic	Rs 10/-

Can you do this without writing?
Guess the total money Kiran will pay to the junk collectors. Will it be
— More than 600?
— Less than 600?

Answer 1

• Cost of 1 kg newspaper = Rs 5

Cost of 31 kg newspaper = Rs 5 × 31
= Rs 155

We do it in the following manner:
5 × 30 = 150
5 × 1 = 5
So,
$$\begin{gathered} \begin{array}{ccc}1& 5& 0\\ +& & 5\end{array} \\ \underline{\overline{\begin{array}{ccc}1& 5& 5\end{array}}} \end{gathered}$$

• Cost of 42 kg newspaper = Rs 5 × 42

= Rs 210
We do it like this:
5 × 40 = 200
5 × 2 = 10
So,
$$\begin{gathered} \begin{array}{ccc}2& 0& 0\\ +& 1& 0\end{array} \\ \underline{\overline{\begin{array}{ccc}2& 1& 0\end{array}}} \end{gathered}$$

(a)
Cost of 1 kg plastic = Rs 10
Cost of 22 kg plastic = 22 × Rs 10
= Rs 220

We do it in the following manner:
22 × 1 = 22
22 × 10 = 220

(b)
Cost of 1 kg waste paper = Rs 4
Cost of 23 kg wastepaper = Rs 4 × 23
= Rs 92

We do it in the following manner:
4 × 20 = 80
4 × 3 = 12
So,
$$\begin{gathered} \begin{array}{ccc}& 8& 0\\ +& 1& 2\end{array} \\ \underline{\overline{\begin{array}{ccc}& 9& 2\end{array}}} \end{gathered}$$

(c)
Cost of 1 kg iron = Rs 12
Cost of 12 kg iron = Rs 12 × 12
= Rs 144

We do it in the following manner:




Add the numbers in the box

$$\begin{gathered} \begin{array}{ccc}1& 0& 0\\ & 2& 0\\ & 2& 0\\ +& & 4\end{array} \\ \underline{\overline{\begin{array}{ccc}1& 4& 4\end{array}}} \end{gathered}$$

Total money paid to junk collectors will be = Rs 155 + Rs 210 + Rs 220 + Rs 92 + Rs 144
= Rs 821

$$\begin{gathered} \begin{array}{cccc}& & & \\ & \stackrel{2}{1}& \stackrel{1}{5}& 5\\ & 2& 1& 0\\ & 2& 2& 0\\ & & 9& 2\\ +& 1& 4& 4\end{array} \\ \underline{\overline{\begin{array}{cccc}& 8& 2& 1\end{array}}} \end{gathered}$$

So, the total money paid to the junk seller is more than Rs 600.