CBSE NCERT Solutions for Class 7 Chapter 9

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CBSE NCERT Solutions for Class 7 Maths Chapter 9:

Question-1:

Find the sum:
(i) 5/4 + (-11/4 )
(ii) 5/3 + 3/5
(iii) -9/10 + 22/15
(iv) -3/ -11 + 5/9
(v) -8/19 + (-2) /57
(vi) -2/3 + 0
(vii) -2 1/3 + 4 3/5

Solution:

(i) 5/4 + (-11/4 ) =(5-11)/4 = -6/4 = -3/2
(ii) 5/3 + 3/5 =(5/3)(5/5) + (3/5)(3/3) = 25/15 + 9/15 [L.C.M. of 3 and 5 is 15]
=(25+9) / 15 = 34/15 = 2 4/15
(iii) -9/10 + 22/15 =(-9/10) (3/3) + (22/15) * (2/2) = -27/30 + 44/30 [L.C.M. of 10 and 15 is 30]
= (-27+44) / 30 = 17/30
(iv) -3/ -11 + 5/9 = (-3/ -11)
(9/9) + (5/9) *(11/11) = 27/99 + 55/99 [L.C.M. of 11 and 9 is 99]
=(27+55) /99 = 82/99
(v) -8/19 + (-2) /57 =(-8/19) *(3/3) + (-2/57) *(1/1) = -24/57 + (-2)/57 [L.C.M. of 19 and 57 is 57]
= (-24 -2 ) / 57 = -26 / 57
(vi) -2/3 + 0 = -2/3
(vii) -2 1/3 + 4 3/5 = -7/3 + 23/5 = (-7/3) *(5/5) + (23/5) *(3/3)
= -35/15 + 69/15 [L.C.M. of 3 and 5 is 15]
=(-35 + 69) /15
= 34/15 = 2 4/15

Question-2:

Find :
(i) 7/24 - 17/36
(ii) 5/63 - (-6/21 )
(iii) -6/13 - (-7/15 )
(iv) -3/8 - 7/11
(v) -2 1/9 -6

Solution:

(i) 7/24 - 17/36 = (7/24) * (3/3) - (17/36) * (2/2) = 21/72 - 34/72 [L.C.M. of 24 and 36 is 72]
21/72 - 34/72 =(21- 34) /72 = -13 / 72
(ii) 5/63 - (-6/21 ) =(5/63)* (1/1) - (-6/21 ) *( 3/3) = 5/63 - (-18)/63 [L.C.M. of 63 and 21 is 63]
[L.C.M. of 63 and 21 is 63]
5/63 - (-18)/63 = (5- (-18)) /63 = (5+18 )/ 63 = 23/63
(iii) -6/13 - (-7/15 ) = (-6 /13 ) (15/15 ) - ( -7 /15) * ( 13/13 ) = -90 / 195 - (-91/195)
[L.C.M. of 13 and 15 is 195]
-90 / 195 - (-91/195) = (-90 – (-91) )/195 = ( -90+91)/ 195 = 1/ 195
(iv) -3/8 - 7/11 = ( - 3/8) * ( 11/11) - (7/11) (8/8) = -33/88 - 56/88 [L.C.M. of 8 and 11 is 88]
[L.C.M. of 8 and 11 is 88]
-33/88 - 56/88 = (-33 – 56 )/88 =-89/88 = -1 1/88
(v) -2 1/9 -6 = -19/9 - 6/1 = (-19/9) * (1/1) – (6/1)
(9/9) [L.C.M. of 9 and 1 is 9]
[L.C.M. of 9 and 1 is 9]
(-19/9) * (1/1) – (6/1)
(9/9) = -19/9 - 54/9 = (-19 – 54)/9 = -73 /9 = -8 1/9