Mathematics: Class 4 — Chapter 7: The Cleanest Village

7.1 My School Trip

Daisy and Lou study in Grade 4 in Shillong, Meghalaya. Their school has organized a field trip to Mawlynnong, known as Asia's Cleanest Village.

Trip Date: December 30, 2025
Cost: $\text{‑ } 500$ per child
Key Attractions: Jingmaham Living Root Bridge, Church of the Epiphany, Mawlynnong Waterfall
Location: East Khasi Hills, $79\text{ km}$ from Shillong
Population: Khasi Tribe ($77$ families, $414$ people)
Activities: Sightseeing, Rich Culture, Nature

7.2 Daisy and Lou Go Shopping

Before the trip, Daisy and Lou join their mother for weekly shopping to buy fruits, vegetables, and field trip items.

Price List (Cost per $1\text{ kg}$)

Custard apple: $\text{‑ } 45$
Beans: $\text{‑ } 95$
Radish: $\text{‑ } 23$
Onion: $\text{‑ } 32$
Potato: $\text{‑ } 37$
Yam: $\text{‑ } 45$
Sapota: $\text{‑ } 70$
Papaya: $\text{‑ } 65$
Banana: $\text{‑ } 55$

Shopping Calculations

Calculate the costs for different quantities:

$2\text{ kg}$ of beans: $2 \times 95 = \text{‑ } 190$
$1\text{ kg}$ of custard apple and $1\text{ kg}$ of sapota: $45 + 70 = \text{‑ } 115$
$1\text{ kg}$ of onion and $1\text{ kg}$ of potato: $32 + 37 = \text{‑ } 69$
$1\text{ kg}$ of radish and $1\text{ kg}$ of yam: $23 + 45 = \text{‑ } 68$
$2\text{ kg}$ of radish and $2\text{ kg}$ of papaya: $2 \times 23 + 2 \times 65 = 46 + 130 = \text{‑ } 176$
$2\text{ kg}$ of onion and $2\text{ kg}$ of potato: $2 \times 32 + 2 \times 37 = 64 + 74 = \text{‑ } 138$

7.3 A Strange Puzzle!

Four kids on a walk buy $2$ oranges each from a farmer. Each orange costs $\text{‑ } 21$. The total cost for each kid is $2 \times 21 = \text{‑ } 42$.

Calculate the balance each kid receives based on the note they paid with:

Krishna: Paid $\text{‑ } 50$ $\rightarrow$ Balance: $50 - 42 = \text{‑ } 8$
Sudama: Paid $\text{‑ } 100$ $\rightarrow$ Balance: $100 - 42 = \text{‑ } 58$
Mala: Paid $\text{‑ } 200$ $\rightarrow$ Balance: $200 - 42 = \text{‑ } 158$
Neela: Paid $\text{‑ } 500$ $\rightarrow$ Balance: $500 - 42 = \text{‑ } 458$

7.4 Let Us Play: Triangle Number Puzzle

Place the numbers $1\text{--}6$ in the circles of a triangle such that the sum of the numbers on each side is equal.

To get a sum of $9$ on each side: Place the smaller numbers $1$, $2$, and $3$ at the corners of the triangle.
To get a sum of $10$ on each side: Place the numbers $4$, $5$, and $6$ at the corners of the triangle.

7.5 Addition with Regrouping

Learn how to add multi-digit numbers by regrouping ones into tens, and tens into hundreds.

Example 1: Teachers Accompanying Children

Add $24$ teachers from one school and $28$ teachers from another school:

$$24 + 28 = 52$$

Regrouping Process: $4\text{ Ones} + 8\text{ Ones} = 12\text{ Ones} = 1\text{ Ten} + 2\text{ Ones}$.

Example 2: Total Children on the Trip

Add $438$ children from one school and $476$ children from another school:

$$438 + 476 = 914$$

Regrouping Process: $8\text{ Ones} + 6\text{ Ones} = 14\text{ Ones} = 1\text{ Ten} + 4\text{ Ones}$. Then, $1\text{ Ten} + 3\text{ Tens} + 7\text{ Tens} = 11\text{ Tens} = 1\text{ Hundred} + 1\text{ Ten}$.

7.6 Subtraction with Regrouping

Learn how to subtract multi-digit numbers by regrouping hundreds into tens, and tens into ones.

Example 1: Comparing Snack Choices

$83$ children bought Pusaw (a traditional Khasi snack made of red rice) and $46$ children bought fruit plates. How many more children bought Pusaw?

$$83 - 46 = 37$$

Regrouping Process: Since $3 < 6$, regroup $1\text{ Ten}$ from $8\text{ Tens}$ to make $13\text{ Ones}$. Then, $13 - 6 = 7\text{ Ones}$ and $7\text{ Tens} - 4\text{ Tens} = 3\text{ Tens}$.

Example 2: Money Spent on Food and Gifts

Lou and Daisy brought $\text{‑ } 310$ in total. They are left with $\text{‑ } 179$. How much money did they spend?

$$310 - 179 = 131$$