One fifth of a number plus three times the number is equal to twice the number plus 42. What is the number? Practice Think: What equation can you write to solve the problem?

For this problem, we will assign the number a letter to represent it: X

One fifth of x + 3 x's equals 42 + 2 x's

Translate that to:

1/5x + 3x = 42 + 2x

Next, use algebra to solve this equation.

Start by multiplying everything by 5 to make all the x values whole numbers:

5x + 15x = 210 + 10x

Next, add common factors of x:

20x = 210 + 10x

Then subtract 10 x's from each side to make only one factor with x:

10x=210

Finally, divide by ten to make only one x:

X=21

The number is 21