Question

The sum of three numbers is $20.$ The first is $4$ times the sum of the other two. The second is seven times the third. What is the product of all three?

Answer 1

let the numbers be

X , y and z

X+ y + z = 20

first number is 4 times the sum of other 2

X = 4(y+ z)

second is 7 times third

y = 7z

now substituting back

X= 4 (7z + z)

X= 32z

32z + 7z + z = 20

40z = 20

z = 1/2

y = 1/2 * 7 = 7/2

X = 1/2 * 32 = 32/2

1/2 * 7/2 * 16 = 28

28 is the answer!