Question

Let the sum of 3 numbers be 13680. If the first number is 3/5 of the third number and the ratio between the second and the third number is 4:7, then the first number is ..?

Answer 1

Answer:

The first number is 3780.

Step-by-step explanation:

x + y + z = 13680

x = 3/5 z

y : z = 4 : 7,  so y = 4/7 z

3/5 z + 4/7 z + z = 13680   / * 35  (we multiply both sides by 35)

21 z + 20 z + 35 z = 478800

76 z = 478800

z = 478800 : 76

z = 6300

x = 3/5 * 6300 = 3780 ( the first number )