12.
The following line graph gives the ratio of the amount of entry to the amount of exit of a
specific molecule from a cell, over the time period 1-7 hours. If the entry at 4 hours was
250 units and the total exit at 4 hours and 5 hours together was 500 units, then the entry at
5 hours was:
a. 250 units
b. 300 units
c. 357 units
d. 420 units

Detailed solution: entry–exit ratio line graph question with options explained

This article provides a clear, step‑by‑step solution to an entry exit ratio line graph question, showing how to use given ratios and totals to find the correct entry value at 5 hours.

Understanding the question

The line graph shows the ratio of entry to exit of a molecule from a cell at each hour from 1 to 7 hours.

• At 4 hours, entry = 250 units.
• The total exit at 4 and 5 hours together = 500 units.
• From the graph, the entry/exit ratio values needed are:
  • At 4 hours: ratio = 1.25
  • At 5 hours: ratio = 1.40

Let:

• E4 = entry at 4 h = 250 units
• X4 = exit at 4 h
• E5 = entry at 5 h (unknown)
• X5 = exit at 5 h

Step‑by‑step calculation

The entry at 5 hours is 420 units, so option (d) is correct.

Explanation of each option

• (a) 250 units
  This is the entry at 4 hours, not at 5 hours, so this confuses the given data with the required value.
• (b) 300 units
  300 units is the exit at 5 hours (found from the total exit condition), not the entry, so this is incorrect.
• (c) 357 units
  This does not satisfy the ratio at 5 hours, because 357/300 = 1.19, not 1.40, so it contradicts the graph.
• (d) 420 units
  This satisfies both the entry/exit ratio at 5 hours (420/300 = 1.40) and the total exit condition, so this is the correct answer.