Question

any 5 rational numbers sums asked in cbse boards

Answer 1

ANSWER .....


THESE ARE MAJOR SUMS THAT ARE ALWAYS ASKED IN CBSE EXAMS.........



The additive inverse of 2/5 is -2/5

Therefore, 4/7 - 2/5 = 4/7 + (-2/5)

⇒ 4/7 - 2/5 = 4 × 5/7 × 5 + (-2) × 7/5 × 7

                = 20/35 + -14/35

                = 20 + (-14)/35

                = 6/35

Therefore, 4/7 - 2/5 = 6/35


2. Subtract -6/7 from -5/8.

Solution:

The additive inverse of -6/7 is 6/7

Therefore, -5/8 - (-6/7) = -5/8 + 6/7, [Since, -(-6/7) = 6/7)]

⇒ -5/8 - (-6/7) = -5 × 7/8 × 7 + 6 × 8/7 × 8

⇒ -5/8 - (-6/7) = -35/56 + 48/56

⇒ -5/8 - (-6/7) = -35 + 48/56

⇒ -5/8 - (-6/7) = 13/56

Therefore, -5/8 - (-6/7) = 13/56

 

3. Subtract -4/9 from 2/5

Solution:

The additive inverse of -4/9 is 4/9.

Therefore, 2/5 - (-4/9) = 2/5 + 4/9, [Since, -(-4/9) = 4/9)]

⇒ 2/5 - (-4/9) = 2 × 9/5 × 9 + 4 × 5/9 × 5

⇒ 2/5 - (-4/9) = 18/45 + 20/45

⇒ 2/5 - (-4/9) = 18 + 20/45

 Therefore, 2/5 - (-4/9) = 38/45


4. The sum of two rational numbers is -3/5. If one of the number is -9/20, find the other.

Solution:

Sum other number = -3/5, One number = -9/20

Therefore, the other number = Sum of the two rational numbers - One of the given rational number.

                                       = -3/5 - (-9/20)

                                       = -3/5 + 9/20, [Since - (-9/20) = 9/20]

                                       = (-3) × 4 + 9 × 1/20

                                       = -12 + 9/20

                                       = -3/20

Therefore, the required rational number is -3/20.


5. Which rational number should be added to -7/11 so as to get 4/7?

Solution:

Su of the given number and the required rational number = 4/7.

Given rational number = -7/11.

Therefore, the required number = Sum - Given number

                                           = 4/7 + 7/11

                                           = 4 × 11/7 ×11 + 7 × 7/11 × 7

                                           = 44/77 + 49/77

                                           = 44 + 49/77

                                           = 93/77

Thus, the rational number 93/77 should be added to -7/11 so as to get 4/7.


6. What should be subtracted from -4/5 so as to get 6/15?

Solution:

Difference of the given rational number and the required rational number = 6/15.

Given rational number = -4/5.

Therefore the required rational number = -4/5 - 6/15

                                                    = -4/5 + -6/15

                                                    = (-4) × 3/5 × 3 + -6/15

                                                    = -12/15 + -6/15

                                                    = (-12) + (-6)/15

                                                    = -18/15

                                                    = -6/5

Thus, the rational number -6/5 subtracted from -4/5 so as to get 6/15.

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