RBSE Solutions for Class 5 Maths Chapter 17 Mental Mathematics

Rajasthan Board RBSE Solutions for Class 5 Maths Chapter 17 Mental Mathematics Textbook Exercise Questions and Answers.

RBSE Class 5 Maths Solutions Chapter 17 Mental Mathematics

InText Questions:

Question 1.
Identify the right answer.

Solution:
(i) Ist number is between 406 and 496 and second number is between the number 30 and 39, then their sum will be between 436 (406 + 30) and 535 (496 + 39). Thus, (a) 483 is correct.

(ii) Ist number is between 390 and 399 and IId number is between 102 and 192, so their sum will be between 492 (390 + 102) and 591(399 + 192). Thus answer will be (a) 495.

Question 2. 
Solve and find the correct option:

(a) 572
(b) 613
(c) 512
Solution: 
In the exercise, the first number is 750 or greater and less than 760, the second number is 205 or greater and less than 295 subtracting 205 or greater from any number less than 760 will not give 572 and also 613 will not be obtained. So, 512 is the correct answer among all the three.

Question 3. 
Identify the appropriate digit which will come in the box.

Solution:
(a) There will be 5 in the first box because adding 5 tens to 8 tens gives 13 tens. Write down 3 tens out of 13 tens and add 10 tens to 4 hundred and 2 hundred, we get 7 hundreds finally.

(b) Similarly,

Exercise 17.1

Question 1.
Mark the right answer (✓).

Solution:

(i) Ist number is between 503 and 593. IInd number is between 50 and 59. So, their sum will lie between 553 (503 + 53) and 652 (593 + 59). Thus, (c) 582 is correct.

(ii) Ist number is between 305 and 395. IInd number is between 280, is between 289. So, their sum will lie between 585 (305 + 280) and 684 (395 + 289). Thus, (b) 597 is correct.

(iii) Ist number is between 4703 and 4793. Ilnd number is between 3080 and 3989. So, their sum will lie between 7783 (4703+ 3080) and (4793 + 3989), Thus, (a) 7807 is correct.

(iv) Ist number is between 700 and 709. IInd number is between 305 and 395. So, their difference lies between 395 (700 - 305) and 314 (709 - 395). Thus, (c) 381, is correct.

(v) Ist number is 864 and other number is between 500, is between 599. Their difference may be between 364 (864 - 500) is between 265 (864 - 599). Thus, (a) 272 is correct.

(vi) Ist number is between 6501 and 6591. IInd number is between 2040 and 2949. So, their difference will lie between 4461 (6501-2040) and 3642 (6591 - 2949), Thus, (b) 4242 is correct.

Question 2.

 
Solution:

Exercise 17.2

Question 1.

Solution:
(i) Ist number may be 5204, ..... 5294.
Other number may be 3060    3969.
Their sum lies between 8264 (5204 + 3060) and 9263 (5294 + 3969). 
Thus, (c) 8491 is correct.

(ii) Ist number may be 8020, .... 8929. Other number may be 4103, 4193. Their sum will be 12123 (8020 + 4103) and 13122 (829 + 4193). 
Thus (a) 12852 is correct.

(iii) Ist number is between 40 to 49 and Ilnd number is between 30 to 40, their total is 70 (40 + 30) and 88 (49 + 39X Hence option (C) 86 is correct.

(iv) Ist number is between 90 to ,99 and IInd number is between 30 and 39. Their difference is between 60(90 - 30)  and 70 (99 - 39), its unit digit will be 6.
Hence option (b) 63 is correct.

(v) Ist number is between 907 and 997 and Ilnd number is between 90 and 99. Their difference will be between 817 (907 - 90) and 898 (997 - 99). Hence, option (C) is correct.

(vi) Ist number is between 8020 and 8929 and Ilnd number is between 4304 and 4394. Their difference will be between 3176 (8020-4304) and 4535 (8929-4394).
Hence option (b) 3942 is correct.

Question 2. 
25 should be multiplied with which one digit number to get a number having 0 at the tens and units place.
Solution: 
Multiplying 25 by 4, 25 × 4 = 100 
Multiplying 25 by 8, 25 × 8 = 200 
Hence, zero is obtained at unit ant tens place, go the number is 4.

Question 3. 
To obtain ten times of a given number, with which number it should be multiplied ?
Solution: 
10 (∵ 10x = 10 times of x)

Question 4. 
Which number when multiplied by 5 gives products having 5 at the units place ?
Solution: 
1, 3, 5, 7 and 9 are the number which gives 5 at unit place, if multiplied by 5.

Question 5. 
To find half of a number, by which number it should be divided.
Solution: 
2 (∵ [latex]\frac{x}{2}[/latex] = half of x)

Question 6. 
Find out a 2-digits number whose both digits are same and the number is divided by 7.
Solution:
77 (∵ 77 ÷ 7 = 11) 

Question 7. 
Find out a number, which divides all numbers.
Solution: 
1 (∵ x ÷ 1 = x)

Question 8. 
What operation we have to apply on 9 and 6. So that we have 54 as the answer.
Solution: 
Multiplication, 9 × 6 = 54

Question 9. 
What operation we have to apply on 6 and 3. So that we have 2 as the answer.
Solution: 
Division 6 × 3 = 2

Question 10. 
Which number when multiplied by any number gives the answer zero ?
Solution: 
Zero (0)

Question 11. 
Find out the smallest number of 2-digitis which is divisible by 2 and 3.
Solution: 
12 is the required number (∵ 12 ÷ 3 = 4 and v 12 ÷ 4 = 3)

 

Important Questions:

Multiple Choice Question: 

Number in blank space will be : . 
Question 1. 
237 + 4 5 = 672
(a) 4    
(b) 3    
(c) 2    
(d) 1
Solution:
(b) 3    

Question 2.    
372 + 6 = 458
(a) 5    
(b) 6    
(c) 7    
(d) 8
Solution:
(d) 8

Question 3.    
475 - 1 3 = 292
(a) 8    
(b) 9    
(c) 7    
(d) 6
Solution:
(a) 8

Question 4.    
 13 + 5 4 = 607
(a) 0, 9 
(b) 0, 7 
(c) 7, 0 
(d) 9, 0
Solution:
(a) 0, 9 

Question 5.    
5  9 - 49  = 78
(a) 5, 1, 0    
(b) 4, 1, 0    .
(c) 6, 1, 0    
(d) 3, 2, 0
Solution:
(c) 6, 1, 0

Question 6.    
4 9 + 212 = 711,
(a) 6    
(b) 7    
(c) 8    
(d) 9 
Solution:
(d) 9 

Question 7.    
4  5 - 30 = 128:
(a) 3, 7 
(b) 3, 6 
(c) 4, 5 
(d) 3, 5
Solution:
(a) 3, 7 

Question 8.    
+ 432 = 821
(a) 489 
(b) 289 
(c) 388 
(d) 389
Solution:
(d) 389

Question 9.    
1273 - = 919
(a) 354 
(b) 254 
(c) 454 
(d) 353
Solution:
(a) 354

Question 10. 
What should be added to 188 to get 276 :
(a) 78 
(b) 88 
(c) 98    
(d) 87
Solution:
(b) 88 

Short Answer Type Questions:

Question 1. 
Fill in the blanks

Solution: 
(1) 9, 3
(2) 0
(3) 3, 8
(4) 2, 6
(5) 149
(6) 0, 1.

Question 2.
By estimating choose correct option write in blank space (total or difference).

Solution:

option (a) 591 is correct.

(b)
 
option (c) 252 is correct.

(c)

option (d) 930 is correct.

Question 3. 
Fill in the blanks:

Solution:

                
Question 4. 
Try the following questions. Each box has number. Write the appropriate number that should be written in it.

Solution:
(1) Digit at hundreds place = 2 in first number and digit at tens place = 6 in second number.
So, it can't be 258 or 500,
so that (a) 362 will be correct answer.

(2) In given numbers 0 is at tens place in first number and 5 at tens place in second number.
So, neither 75 nor 165 can be remain and subtracting one number from other number.

(3) In given numbers, 2 is at hundreds place in first number and 1 is at hundreds place in second number. On subtracting one number from other neither 312 nor 459 remains i.e. answer will be (a) 142.

Question 5. 
When number remains same when multiplied by any number? 
Solution: 
Required number is 1.

Question 6. 
Find two digit least number which is divisible by 3 and 4 both.
Solution: 
10, 11, 12, ........... 12 is least two digit number which is divisible by 3 and 4 both.

Question 7. 
What operation is used between 5 and 7 so that we get 3 at tens place ?
Solution: 
Multiplication operation, 5 × 7 = 35.

Question 8.
25 is multiplied by which one digit number so that in answer we get 2 at hundred place?
Solution: 
Required number are 8 and 9 because 25 × 8 = 200 and 25 × 9 = 225