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Chapter 1

Number System — Mental Maths

Class - 6 RS Aggarwal Mathematics Solutions



Exercise 1(F) — Mental Maths

Question 1

Fill in the blanks with > or < :

(i) 4,80,798 ............... 4,81,612

(ii) 5,43,611 ............... 5,43,584

(iii) 2,37,928 ............... 68,946

Answer

(i) 4,80,798 ............... 4,81,612

Both numbers have 6 digits.

Comparing from the left:

The lakhs digit is 4 in both.

The ten thousands digit is 8 in both.

The thousands digit is 0 in 4,80,798 and 1 in 4,81,612.

Since 0 is less than 1, 4,80,798 is smaller than 4,81,612.

Hence, 4,80,798 < 4,81,612.

(ii) 5,43,611 ............... 5,43,584

Both numbers have 6 digits.

Comparing from the left:

The lakhs digit is 5 in both.

The ten thousands digit is 4 in both.

The thousands digit is 3 in both.

The hundreds digit is 6 in 5,43,611 and 5 in 5,43,584.

Since 6 is greater than 5, 5,43,611 is larger than 5,43,584.

Hence, 5,43,611 > 5,43,584.

(iii) 2,37,928 ............... 68,946

2,37,928 has 6 digits.

68,946 has 5 digits.

A number with more digits (when positive) is always greater than a number with fewer digits.

Hence, 2,37,928 > 68,946.

Question 2

Fill in the blanks :

(i) 839 rounded to nearest hundred is ...............

(ii) 83,867 rounded to nearest thousand is ...............

(iii) (368 + 143) to nearest ten is ...............

Answer

(i) The tens digit is 3, which is less than 5, so we round down.

Hence, 839 rounded to the nearest hundred is 800.

(ii) The hundreds digit is 8, which is 5 or greater, so we round up the thousands digit.

Hence, 83,867 rounded to the nearest thousand is 84,000.

(iii) The sum: 368 + 143 = 511.

Then, round 511 to the nearest ten. The units digit is 1, which is less than 5, so we round down.

Hence, 368 + 143 to the nearest ten is 510.

Question 3(i)

Write True or False :

0 is the smallest counting number.

Answer

False.

Reason

Counting numbers (also known as natural numbers) are the numbers we use for counting objects. They start from 1.

0 is a whole number, but not a counting number in the mathematical sense.

Question 3(ii)

Write True or False :

The 8th place in the Indian place value chart is called Ten Lakh.

Answer

False

Reason

In the Indian place value chart, starting from the right (ones place):

  1. Ones

  2. Tens

  3. Hundreds

  4. Thousands

  5. Ten Thousands

  6. Lakhs

  7. Ten Lakhs

  8. Crores

So, the 8th place is called Crores, and the 7th place is called Ten Lakhs.

Question 3(iii)

Write True or False :

10 lakhs make a million.

Answer

True

Reason

In the Indian Numbering System: 10 Lakhs = 10,00,000

In the International Numbering System: 1 Million = 1,000,000

Both represent the same value.

Question 3(iv)

Write True or False :

The predecessor of the smallest 7-digit number is the largest 6-digit number

Answer

True

Reason

The smallest number that has 7 digits = 1,000,000 (one million or ten lakh).

The predecessor of a number is the number that comes immediately before it.

Predecessor of 1,000,000 = 1,000,000 - 1 = 999,999.

The largest number that has 6 digits = 999,999.

The predecessor of the smallest 7-digit number = 999,999.

The largest 6-digit number is 999,999.

Question 3(v)

Write True or False :

10 millions make a crore.

Answer

True

Reason

International System: 10 million = 10,000,000

Indian System: 1 crore = 1,00,00,000

Since 10,000,000 (10 million) is equal to 1,00,00,000 (1 crore).

Question 3(vi)

Write True or False :

13,564,030 in International system is written as thirteen million five hundred sixty four thousand thirty.

Answer

True

Reason

Here's the breakdown of 13,564,030 in the International System:

13, (Millions period) - Thirteen million

564, (Thousands period) - Five hundred sixty-four thousand

030 (Ones period) - Thirty

So, 13,564,030 in International system is written as thirteen million five hundred sixty four thousand thirty.

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