CBSE Class 7 Mathematics Large Numbers Around Us Worksheet Set 01

Very Short Answer Questions

Question 1. Write the smallest 6-digit number in figures and also in words.
Answer:
In figures: 1,00,000. In words: one lakh.

Teacher's Note:
1. It is 99,999 + 1.
2. Place the comma after the lakhs digit.

Question 2. Write the number 7,00,905 in words in the Indian system.
Answer:
7 | 00 | 905 is read as seven lakh nine hundred five.

Teacher's Note:
1. The thousands group is 00, so no thousands are named.
2. Read group by group.

Question 3. Write in figures: Nine lakh sixty thousand forty.
Answer:
9 lakh | 60 thousand | 040 gives 9,60,040.

Teacher's Note:
1. 'Forty' sits in the tens place: 040.
2. Fill empty places with zeroes.

Question 4. The Statue of Unity is about 180 m tall and Somu’s building is about 40 m tall. How much taller is the statue than the building?
Answer:
180 − 40 = 140, so the statue is 140 m taller.

Teacher's Note:
1. 'How much taller' means subtract.
2. 'How many times' would mean divide.

Question 5. A calculator has only a +1000 button. How many times must it be pressed to show 90,000?
Answer:
Each press adds 1000: 90,000 ÷ 1000 = 90 times.

Teacher's Note:
1. Presses = number ÷ button value.
2. Dividing by 1000 removes three zeroes.

Question 6. How many hundreds are required to make one lakh?
Answer:
1,00,000 ÷ 100 = 1000, so 1000 hundreds make one lakh.

Teacher's Note:
1. 100 hundreds make ten thousand.
2. Ten times that makes one lakh.

Question 7. How many zeroes are there in one crore? Write one crore in figures.
Answer:
One crore has 7 zeroes: 1,00,00,000.

Teacher's Note:
1. A crore is 100 lakh.
2. Lakh has 5 zeroes; add two more.

Question 8. Write one million in the Indian place value system and give its Indian name.
Answer:
One million = 10,00,000, which is ten lakh.

Teacher's Note:
1. Million has 6 zeroes.
2. Put the commas in the 3-2-2 way.

Question 9. How are the digits of a large number grouped by commas in the American (International) system?
Answer:
Commas come after every three digits from the right (3-3-3 pattern), giving thousands, millions and billions.

Teacher's Note:
1. The Indian system uses 3 then 2-2-2.
2. Example: 9,876,501,234.

Question 10. Round off 8,473 to the nearest hundred.
Answer:
The tens digit is 7, which is 5 or more, so round up: 8,500.

Teacher's Note:
1. For hundreds, look at the tens digit.
2. 8,473 is between 8,400 and 8,500.

Question 11. Why is multiplying a number by 5 the same as dividing it by 2 and then multiplying by 10?
Answer:
Because 5 = 10 ÷ 2. Halving and then multiplying by 10 multiplies the number by 10 ÷ 2 = 5.

Teacher's Note:
1. Halving and adding a zero is quick.
2. Check: 18 × 5 = 9 × 10 = 90.

Question 12. The distance between the Earth and the Moon is 3,84,400 km. Write this number in words.
Answer:
Three lakh eighty four thousand four hundred kilometres.

Teacher's Note:
1. 3 | 84 | 400: lakh, thousand, hundreds.
2. Read each group with its name.

Question 13. If a person tastes 3 new varieties of rice every day, how many varieties will they taste in 100 years? Take 365 days in a year.
Answer:
Varieties = 3 × 365 × 100 = 1,09,500. So they would just cross one lakh varieties.

Teacher's Note:
1. First find the days in 100 years: 36,500.
2. Then multiply by 3.

Question 14. Roughly how many years is one lakh days? Show the division you use.
Answer:
1,00,000 ÷ 365 ≈ 274, so one lakh days is about 274 years, far more than a normal lifetime.

Teacher's Note:
1. Divide days by 365 to get years.
2. A rough answer is enough here.

Question 15. A calculator has only a +10 button. How many times must it be pressed to show one lakh?
Answer:
1,00,000 ÷ 10 = 10,000 times.

Teacher's Note:
1. Small buttons need many presses.
2. Dividing by 10 removes one zero.

Question 16. Write the expression for 40,629 that uses the least number of button clicks on Systematic Sippy, and state how many clicks it needs.
Answer:
40,629 = (4 × 10000) + (6 × 100) + (2 × 10) + (9 × 1).
Clicks = 4 + 6 + 2 + 9 = 21, the sum of the digits.

Teacher's Note:
1. The zero in the thousands place needs no clicks.
2. Least clicks = sum of the digits.

Question 17. Insert commas in 50607080 using the Indian system and write its number name.
Answer:
5,06,07,080: five crore six lakh seven thousand eighty.

Teacher's Note:
1. From the right: 3 digits, then 2, then 2.
2. Read each group with its name.

Question 18. Fill in the blank with <, > or = : 90 lakh ______ 9 million.
Answer:
90 lakh = 90,00,000 and 9 million = 9,000,000 = 90,00,000. So 90 lakh = 9 million.

Teacher's Note:
1. 10 lakh = 1 million.
2. So 90 lakh = 9 million.

Question 19. How many lakhs make one billion?
Answer:
One billion = 1,00,00,00,000, and 1,00,00,00,000 ÷ 1,00,000 = 10,000 lakh.

Teacher's Note:
1. 1 billion = 100 crore and 1 crore = 100 lakh.
2. 100 × 100 = 10,000.

Question 20. Write the nearest ten lakh of 6,48,32,119.
Answer:
The lakhs digit is 8, which is 5 or more, so round up: 6,50,00,000.

Teacher's Note:
1. For ten lakh, look at the lakhs digit.
2. The number is between 6,40,00,000 and 6,50,00,000.

Question 21. Estimate 3,47,560 + 2,81,230 by first rounding each number off to the nearest lakh.
Answer:
3,47,560 ≈ 3,00,000 and 2,81,230 ≈ 3,00,000.
Estimated sum = 6,00,000. (The exact sum is 6,28,790.)

Teacher's Note:
1. Round first, then add.
2. An estimate helps check the exact answer.

Question 22. Find 72 × 125 by a quick method.
Answer:
125 = 1000 ÷ 8, so 72 × 125 = \( \frac{72}{8} \) × 1000 = 9 × 1000 = 9000.

Teacher's Note:
1. Multiplying by 125 = dividing by 8 and multiplying by 1000.
2. Works neatly when the number is a multiple of 8.

Question 23. How many digits can the product of two 5-digit numbers have?
Answer:
It can have 9 or 10 digits.
The smallest product, 10,000 × 10,000 = 10,00,00,000, has 9 digits; every product is less than 1,00,000 × 1,00,000, which has 11 digits.

Teacher's Note:
1. Rule: m + n − 1 or m + n digits.
2. Here 5 + 5 − 1 = 9 or 5 + 5 = 10.

Question 24. A large ship can carry about 2,500 passengers. How many people can 5,000 such ships carry together?
Answer:
2500 × 5000 = 1,25,00,000, that is one crore twenty five lakh people.

Teacher's Note:
1. 25 × 5 = 125, then add five zeroes.
2. Count zeroes carefully.

Question 25. Creative Chitti presses +1000 five times, +100 ten times and +1 seventy two times. Which number appears on its screen?
Answer:
(5 × 1000) + (10 × 100) + (72 × 1) = 5000 + 1000 + 72 = 6072.

Teacher's Note:
1. Ten hundreds make one thousand.
2. Add all the parts.

Question 26. A number becomes 7,00,000 when it is rounded off to the nearest lakh. What is the smallest whole number it can be?
Answer:
6,50,000. Numbers from 6,50,000 to 7,49,999 round to 7,00,000, while 6,49,999 rounds to 6,00,000.

Teacher's Note:
1. The halfway number 6,50,000 rounds up.
2. Check the number just below it.

Question 27. Without multiplying, state how many digits the product 6400 × 62,500 can have. Then write the product.
Answer:
6400 has 4 digits and 62,500 has 5, so the product has 4 + 5 − 1 = 8 or 4 + 5 = 9 digits.
6400 × 62,500 = 40,00,00,000, which has 9 digits.

Teacher's Note:
1. 64 × 625 = 40,000; then add four zeroes.
2. Count the digits to check.

Question 28. If you count one coin every second without stopping, how many coins can you count in one day? Can you count one million coins in a day?
Answer:
Seconds in a day = 60 × 60 × 24 = 86,400, so you can count only 86,400 coins.
This is less than 10,00,000, so no, one million coins cannot be counted in a day.

Teacher's Note:
1. Work in stages: minute, hour, day.
2. 1 million = 10 lakh.

Question 29. Using each of the digits 0 to 9 exactly once, write the smallest 10-digit number (the first digit cannot be 0) with Indian commas.
Answer:
Smallest number: 1023456789, written as 1,02,34,56,789.

Teacher's Note:
1. Put 1 first, then 0, then the rest in increasing order.
2. Use the 3-2-2-2 comma pattern.

Question 30. A stadium can seat 1,20,000 people. About how many such stadiums would be needed to seat the whole 2011 population of Mumbai, 1,24,42,373?
Answer:
1,24,42,373 ÷ 1,20,000 ≈ 103.7, so about 104 stadiums would be needed.

Teacher's Note:
1. Round up, since a part of a stadium is not enough.
2. Rough check: 124 lakh ÷ 1.2 lakh ≈ 103.