The ratio of the numerator and denominator of a rational number is 2 : 7 and if 4 is added to the numerator and 2 is subtracted from denominator, the
rational number becomes 10
19
. Find the original rational number.

6/21.

Step-by-step explanation:

let the rational number be 2x/7x.

2x + 4 / 7x - 2 = 10 /19

Cross multiply:

19(2x + 4) = 10(7x - 2)

38x + 76 = 70x - 20

96 = 70x - 38x

32x = 96

x = 3.

So the rational number is  2*3/ 7*3

= 6/21.

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answer: d.) the total number of protons and neutrons is 15

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