Answer:
52/21
Explanation:
Translate the word equation into an algebraic equation as follows:
Let the number be X
two-and-a-half of a number --> (2 1/2) X
2 1/2 = (2 x 2 + 1) = 5/2
So two-and-a-half of a number --> (9/2)X = 9X/2
three-quarters of the same number --> (3/4)X --> 3X/4
two and half of a number added to three quarters of the same number becomes 9X/2 + 3X/4
gives you 13 --> = 13
So we get the equation:
9X/2 + 3X/4 = 13
Multiply both sides by 4 to get rid of the denominators
4.(9X/2) + 4(3X/4) = 4 x 13 = 52
36X/2 + 12X/4 = 52
==> 18X + 3X = 52
==> 21X = 52
==> X = 52/21