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Vilka [71]
3 years ago
14

If 20 is added to one-third of a number, the result is the double of the number. What is the number?

Mathematics
2 answers:
olganol [36]3 years ago
6 0
One third of an unknown number is \frac{1}{3} x.  The word "of" means to multiply.  So if we add 20 to that, and it is equal to double the unknown (that is 2x), the equation looks like this: 20+ \frac{1}{3}x=2x.  Start by multiplying everything by 3 to get rid of the fraction and get 60 + x = 6x.  Now subtract an x from both sides and get 60 = 5x and x = 12.  So the number is 12
Thepotemich [5.8K]3 years ago
3 0
1/3 of an unknown number is 1/3x.  The word "of" lets us know to multiply.  So if we add 20 to that, and it is equal to double x (that is 2x), the equation looks like this: 

1. Start by multiplying everything by 3 to get rid of the fraction and get 20 + 1/3x = 2x.
2. Now subtract an x from both sides and get 60 = 5x and x = 12. 
So the answer is 12
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Answer:

1. Steve's age is 18 and Anne's age is 8.

2. Max's age is 17 and Bert's age is 11.

3. Sury's age is 19 and Billy's age is 9.

4. The man's age is 30 and his son's age is 10.

Step-by-step explanation:

1. Let us assume that:

S = Steve's age now

A = Anne's age now

Therefore, in four years, we have:

S + 4 = (A + 4)2 - 2

S + 4 = 2A + 8 - 2

S + 4 = 2A + 6 .................. (1)

Three years ago, we have:

S - 3 = (A - 3)3

S - 3 = 3A - 9 ................................ (2)

From equation (2), we have:

S = 3A - 9 + 3

S = 3A – 6 …………. (3)

Substitute S from equation (3) into equation (1) and solve for A, we have:

3A – 6 + 4 = 2A + 6

3A – 2A = 6 + 6 – 4

A = 8

Substitute A = 8 into equation (3), we have:

S = (3 * 8) – 6

S = 24 – 6

S = 18

Therefore, Steve's age is 18 while Anne's age is 8.

2. Let us assume that:

M = Max's age now

B = Bert's age now

Therefore, five years ago, we have:

M - 5 = (B - 5)2

M - 5 = 2B - 10 .......................... (4)

A year from now, we have:

(M + 1) + (B + 1) = 30

M + 1 + B + 1 = 30

M + B + 2 = 30 .......................... (5)

From equation (5), we have:

M = 30 – 2 – B

M = 28 – B …………………… (6)

Substitute M from equation (6) into equation (4) and solve for B, we have:

28 – B – 5 = 2B – 10

28 – 5 + 10 = 2B + B

33 = 3B

B = 33 / 3

B = 11

Substituting B = 11 into equation (6), we have:

M = 28 – 11

M = 17

Therefore, Max's age is 17 while Bert's age is 11.

3. Let us assume that:

S = Sury's age now

B = Billy's age now

Therefore, now, we have:

S = B + 10 ................................ (7)

Next year, we have:

S + 1 = (B + 1)2

S + 1 = 2B + 2 .......................... (8)

Substituting S from equation (7) into equation (8) and solve for B, we have:

B + 10 + 1 = 2B + 2

10 + 1 – 2 = 2B – B

B = 9

Substituting B = 9 into equation (7), we have:

S = 9 + 10

S = 19

Therefore, Sury's age is 19 while Billy's age is 9.

4. Let us assume that:

M = The man's age now

S = His son's age now

Therefore, now, we have:

M = 3S ................................... (9)

Five years ago, we have:

M - 5 = (S - 5)5

M - 5 = 5S - 25 ................ (10)

Substituting M from equation (9) into equation (10) and solve for S, we have:

3S - 5 = 5S – 25

3S – 5S = - 25 + 5

-2S = - 20

S = -20 / -2

S = 10

Substituting S = 10 into equation (9), we have:

M = 3 * 10

M = 30

Therefore, the man's age is 30 and his son's age is 10.

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