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23 April, 07:25

If 3a+4b = 4a-4b = 21 find the value of a

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Answers (2)
  1. 23 April, 08:31
    0
    A-4b=4b

    a=8b

    Plug it in:

    24b+4b=21

    28b=21

    b=21/28

    a=8b=6.
  2. 23 April, 10:33
    0
    Using the 2nd and 3rd you have:

    4a-4b=21

    4a=21+4b

    a = (21+4b) / 4

    now using 1st and 2nd

    3 (21+4b) / 4+4b=4 (21+4b) / 4-4b

    (63+12b+16b) / 4 = (84+16b-16b) / 4

    63+28b=84

    28b=21

    b=21/28

    b=3/4

    ... now using 4a-4b=21 we have

    4a-4 (3/4) = 21

    4a=3=21

    4a=24

    a=6
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