Step-by-step solved numerical problems on Endocrine for NEET and CBSE.

Endocrine: Numerical Problems Solved Step-by-Step

When we work on Endocrine, numerical problems trip up even strong students — not because the biology is hard, but because the arithmetic setup gets messy. Let’s solve a few together the way a tutor would at the board.

Question 1 — Setting Up Ratios

A population study on endocrine gives us 240 observed units in one sample and 180 in another. If the expected ratio is 4:3, are the samples matching expectation?

Total observed $= 240 + 180 = 420$ . Expected in 4:3 split $= \frac{4}{7} \times 420 = 240$ and $\frac{3}{7} \times 420 = 180$ .

Observed matches expected exactly. The chi-square value $\chi^2 = \sum \frac{(O-E)^2}{E} = 0$ , so the null hypothesis holds.

The samples fit the 4:3 expectation perfectly. In NEET and CBSE problems on endocrine, always convert ratios to fractions of the total before comparing — that’s the step most students skip.

Question 2 — Percentage Calculations

In a endocrine experiment, 85 out of 340 units show a particular trait. What percentage does that represent, and what does it tell us?

$\frac{85}{340} \times 100 = 25\%$ .

A 25% frequency is exactly what we’d expect from a monohybrid cross recessive phenotype ( $\frac{1}{4}$ ), which tells us the trait is likely controlled by a single recessive allele.

25% — and more importantly, the number points to single-gene recessive inheritance. NEET loves this kind of reverse-engineering from data.

Question 3 — Rate Problem

If a process in endocrine proceeds at $2.5$ units per minute and we need $75$ units, how long does it take? What if the rate drops to $60\%$ due to a limiting factor?

Time $= \frac{75}{2.5} = 30$ minutes.

New rate $= 2.5 \times 0.60 = 1.5$ units/min. Time $= \frac{75}{1.5} = 50$ minutes.

30 minutes normally, 50 minutes with the limiting factor. Remember: biological rates rarely stay constant — temperature, pH, and substrate concentration all shift them.

For any numerical in Endocrine, write down what’s given, what’s asked, and the formula — in that order — before touching a calculator. Half the errors come from jumping to computation.

Question 4 — Working Backwards

We observe a final value of $128$ after $3$ doubling cycles. What was the starting value?

Final $=$ Initial $\times 2^n$ , so $128 = x \times 2^3 = 8x$ .

$x = \frac{128}{8} = 16$ .

Starting value was 16. Exponential growth patterns in endocrine almost always reduce to $N = N_0 \times 2^n$ — memorise it.

Common Setup Mistakes

Students mix up ratio and percentage — a 3:1 ratio is 75:25, not 30:10. Always check the denominators add to the total.

These four problems cover the main numerical patterns you’ll face in Endocrine: ratios, percentages, rates, and exponential models. PYQs from the last five years of NEET have all followed this structure, so the weightage on practising them is high.