Q.A consumer has a monthly income of Rs. 600 to spend entirely on two goods X (price Rs. 60 per unit) and Y (price Rs. 40 per unit). Write the budget line equation, find both intercepts, and state its slope.

The budget line equation is Px.x + Py.y = M; set each variable to zero in turn to find the two intercepts, and the slope is −Px/Py.

The budget line equation is $P_x \cdot x + P_y \cdot y = M$. Substituting the given values ($P_x=60,\ P_y=40,\ M=600$):

X-intercept (all income spent on X, so $y=0$): $60x=600 \Rightarrow x=10$ units — the maximum X the consumer could buy.

Y-intercept (all income spent on Y, so $x=0$): $40y=600 \Rightarrow y=15$ units — the maximum Y the consumer could buy. …

Writing the equation with the prices attached to the wrong quantity (e.g. $P_x \cdot y + P_y \cdot x = M$) reverses which intercept belongs to which axis. Computing the slope as $-P_y/P_x$ instead of $-P_x/P_y$ is another frequent inversion error — the coefficient of $x …