Direct variation is a relationship between two variables in which one variable is a constant multiple of the other. When one variable changes, the other variable changes proportionally. The formula for direct variation is y = kx, where y and x are the two varying quantities and k is the constant of proportionality. The graph of two quantities in direct variation will result in a straight line, and the ratio of change (Δy/Δx) is equal to k, which represents the slope of the line. To solve a direct variation problem, we can use the formula y = kx and substitute the given values to find the constant of proportionality k. Once we have k, we can write the direct variation equation and use it to find other values.