DSSSB Pharmacist: Arithmetical & Numerical Ability for DSSSB Pharmacist

Arithmetical & Numerical Ability contributes 20 Tier-I questions. It tests speed and accuracy in number system, simplification, HCF-LCM, percentage, ratio and proportion, average, profit and loss, simple and compound interest, time and work, speed and distance, mensuration, basic geometry and data interpretation. The paper is not advanced mathematics; it applies a small set of formulas to practical situations.

Core formulas

Percentage change = (new value - old value) / old value x 100. Profit% = profit / CP x 100; discount is always calculated on the marked price. SI = PRT/100; CI = P[(1 + R/100)^T - 1]. If a person finishes work in n days, one day's work is 1/n; combined work is 1/a + 1/b. Speed = distance/time; average speed for equal distances is 2xy/(x + y). Mensuration: circle area = pi r squared, circumference = 2 pi r; cylinder volume = pi r squared h; sphere volume = 4/3 pi r cubed.

Worked example

A shopkeeper marks an article 40% above cost and gives a 25% discount. Find the profit percentage. Take CP = 100. Marked price = 140. Discount = 25% of 140 = 35. Selling price = 140 - 35 = 105. Profit = 5 on a cost of 100, so profit = 5%. The reasoning shows why mark-up and discount do not cancel: the discount applies to the marked price, not the cost price.

Traps

Adding successive percentage changes instead of multiplying; applying discount to CP; using the SI formula for CI; taking the arithmetic mean for average speed; mixing centimetres with metres or minutes with hours; and ignoring BODMAS order, especially brackets and division before multiplication.