Average Questions for SSC CHSL

What is Average

Average means the equal share each person would get if the total is distributed equally. Think of it as a balancing point. If 5 friends pool money and split equally, that equal share is the average. In SSC CHSL, the average formula is the starting point for almost every question in this topic.

• Average = Sum of all items divided by number of items
• Sum = Average multiplied by Number of items — this is the most used rearrangement
• Number of items = Sum divided by Average
• Always identify what is given: average, sum, or count — then find the missing one
• Average is always between the smallest and largest value in the group

Average of Consecutive Numbers

For consecutive numbers, consecutive even numbers, or consecutive odd numbers, the average is always the middle value. This is a huge time saver in SSC CHSL. No need to add all numbers. Just find the middle term directly.

• Average of consecutive integers from a to b = (a + b) / 2
• Average of first n natural numbers = (n + 1) / 2
• Average of first n even numbers = n + 1
• Average of first n odd numbers = n
• For any evenly spaced series, average = (first term + last term) / 2

Effect of Adding or Removing a Member

A very common SSC CHSL question type: the average of a group changes when one person joins or leaves. The trick is to use Sum = Average x n before and after the change, then find the new or removed value. This is the single most tested pattern in CHSL average questions.

• Old Sum = Old Average x Old Count
• New Sum = New Average x New Count
• Removed value = Old Sum - New Sum
• Added value = New Sum - Old Sum
• If average increases after adding a member, the new member's value is above the old average
• If average decreases after adding a member, the new member's value is below the old average

Replacement Effect on Average

Another common CHSL pattern: one member of a group is replaced by another. The average changes slightly. Use the change in average to find the new or old value. Think of it as: the total changes by the difference between the two people.

• If average increases by x after replacement, new person's value = old person's value + (n x x)
• If average decreases by x after replacement, new person's value = old person's value - (n x x)
• Change in total = Change in average x total count
• This type often appears in age or weight problems in CHSL

Weighted Average

When two groups are combined and each group has its own average and count, you cannot just average the two averages. You must find total sum of both groups, then divide by total count. SSC CHSL tests this in combined class, mixed group, or journey speed questions.

• Weighted Average = (n1 x A1 + n2 x A2) / (n1 + n2)
• The combined average is always between A1 and A2, never outside
• If group sizes are equal, weighted average = simple average of A1 and A2
• Used in mixture, profit combined, or average speed problems too

• Using n as old count when adding a member — remember new count is n+1, not n
• Simply averaging two averages when group sizes differ — always calculate separate sums first
• Forgetting that average of first n odd numbers is n, not n/2 — students confuse this with natural numbers
• In replacement questions, applying the change in average directly without multiplying by n
• Not reading whether average increased or decreased — a sign error flips the entire answer

• SAN triangle: Sum = Average x N. Cover any one to find the others. Like the speed-distance-time triangle.
• PLUS means bigger: if someone joins and average goes UP, new person is PLUS above the old average. Simple logic check.
• Replacement shortcut memory hook: CHAIN — Change in average x n = difference between new and old person.
• First n ODD numbers average = n itself. Odd and n — both short, both same. First n EVEN average = n+1, one step ahead.

• In CHSL, averages questions are mostly 1-step or 2-step. If your solution has more than 3 steps, recheck your approach — you are likely overthinking it.
• Age-based average questions (family, class, team) are the most common avatar of this topic in recent CHSL papers. Practice at least 10 such PYQs.
• Replacement-type questions appear frequently in Tier 1. They can be solved in under 30 seconds using the change x n shortcut.
• Weighted average sometimes appears disguised as a speed problem — average speed of a journey with two different speeds. Apply the same weighted formula.
• CHSL does not usually test very large datasets or complex multi-group problems. If a question looks very complex, look for a shortcut — there almost always is one.