Why this topic matters · 6 min read
Average is a high-frequency topic in UP Police Constable quant section, appearing in 2-3 questions per paper. Questions test basic average calculation, finding missing numbers, and weighted averages. Difficulty is easy to moderate. Aspirants must master quick mental calculation and spot common traps like confusing total with average.
What is Average?
Average (or arithmetic mean) is the sum of all values divided by the count of values. Think of it as 'fair share' — if you pool all money and distribute equally, everyone gets the average. In UP Police exams, average questions often disguise themselves as word problems about ages, salaries, marks, or distances. The core formula never changes, but the context does.
- Average = Total Sum / Number of Items
- Rearranged: Total Sum = Average × Number of Items
- Average is always between the smallest and largest value in the set
- If all values are equal, average equals that value
- Average can be a decimal or fraction, not always a whole number
Key formulas
Basic Average Formula
Average = (a1 + a2 + a3 + ... + an) / n
When: When you have all values and need to find average
Finding Total from Average
Total = Average × Count
When: When you know average and count, need to find sum (most common in UP Police)
Finding Missing Value
Missing Value = (Average × Count) - (Sum of Known Values)
When: When one value is missing and you know average of all
Worked examples
Example 1: Average of 5 numbers is 20. What is their total? Answer: Total = 20 × 5 = 100. (This type appears frequently in UP Police — they give average and count, ask for total or vice versa.)
Example 2: 4 students scored 60, 75, 80, and X marks. Average is 72. Find X. Solution: Total = 72 × 4 = 288. Sum of known = 60 + 75 + 80 = 215. So X = 288 - 215 = 73.
Average in Word Problems
UP Police loves disguising average in real-world contexts. A question might ask about average age of a group, average salary, average distance traveled, or average marks. The trick is to identify that it's an average problem, extract the numbers, and apply the formula. Read carefully for keywords like 'on average', 'mean', 'equally', or 'fair share'.
- Identify the keyword: 'average', 'mean', 'on average', 'equally distributed'
- Extract: what are we averaging (ages, salaries, marks)?
- Count: how many items are in the group?
- Calculate: use Total = Average × Count or vice versa
- Check: does your answer make sense (between min and max)?
Weighted Average
Sometimes items in a group have different importance or frequency. For example, if 3 students scored 80 and 2 students scored 90, the average is not (80 + 90) / 2 = 85. Instead, you weight by frequency: (80×3 + 90×2) / (3+2) = (240 + 180) / 5 = 84. UP Police occasionally tests this in moderate-difficulty questions. The key is to multiply each value by its weight (frequency or quantity) before summing.
- Weighted Average = (Sum of (Value × Weight)) / (Sum of Weights)
- Weight can be frequency, quantity, or importance
- Always multiply value by its weight before adding
- Divide by total weight, not by number of distinct values
- Common in salary, age, or marks problems with groups
Key formulas
Weighted Average Formula
Weighted Avg = (v1*w1 + v2*w2 + ... + vn*wn) / (w1 + w2 + ... + wn)
When: When different values have different frequencies or weights
Worked example
Example: Group A has 5 people with average age 30. Group B has 3 people with average age 40. Find combined average. Solution: Total age = (30×5) + (40×3) = 150 + 120 = 270. Total people = 5 + 3 = 8. Average = 270 / 8 = 33.75 years.
Average Increase/Decrease
A common UP Police pattern: 'Average was X, then a new person/item joined, average became Y. Find the new person's value.' Or: 'Average was X, one person left, average became Y. Find that person's value.' These require you to calculate totals before and after, then find the difference.
- Calculate old total: old average × old count
- Calculate new total: new average × new count
- Difference = new total - old total = value of person who joined/left
- If average increases, the new person has above-average value
- If average decreases, the new person has below-average value
Worked example
Example: Average age of 4 people is 25 years. A 5th person joins, average becomes 26. Find the 5th person's age. Solution: Old total = 25 × 4 = 100. New total = 26 × 5 = 130. 5th person's age = 130 - 100 = 30 years.
⚠ Common mistakes to avoid
- Confusing average with total: If average is 50 and count is 10, total is 500, NOT 50. Many aspirants forget to multiply.
- Forgetting to count correctly: In weighted average, the denominator is total weight, not number of groups. If 3 people have age 25 and 2 people have age 30, denominator is 5, not 2.
- Assuming average is always a whole number: Average can be 33.75 or 42.5. Don't round unless the question asks.
- Misreading 'per' or 'each': 'Average salary per person' means total salary / number of people. Don't mix up the direction.
- Ignoring the range check: If smallest value is 10 and largest is 50, average must be between 10 and 50. If your answer is 60, you made an error.
🧠 Memory aids
- AVERAGE = TOTAL / COUNT. Rearranged: TOTAL = AVERAGE × COUNT. (This is the golden rule — memorize both directions.)
- Think 'Fair Share': Average is what everyone gets if you pool and divide equally. Helps you sense-check answers.
- Weighted Average = (Value × Weight) summed, then divided by total weight. Mnemonic: VW over W (Value-Weight over total Weight).
- Increase/Decrease: New Total - Old Total = New Person's Value. (Subtract the totals, not the averages.)
🎯 UP POLICE CONSTABLE exam tips
- UP Police typically asks 2-3 average questions per paper, mostly easy to moderate. Expect at least one word problem disguised as a real-world scenario (ages, salaries, distances).
- Time management: Average questions should take 1-2 minutes max. If you're stuck, move on and come back. These are not meant to be time-sinks.
- Watch for multi-step problems: A question might ask average, then ask 'if one person leaves, what is new average?' Practice these chains.
- Weighted average is less common but appears in 1 in 5 papers. If you see 'groups' or 'frequencies', think weighted average immediately.
- Calculators are NOT allowed in UP Police. Practice mental math for multiplication and division. For example, 26 × 5 should be instant (130).
Q1 · medium · PYQ 2009
एक कक्षा के 20 छात्रों का औसत वजन 21 कि०ग्रा० है। यदि उनमें अध्यापक का भी वजन सम्मिलित कर लिया जाय तो उनका औसत वजन एक कि०ग्रा० और अधिक हो जाता है। तो अध्यापक का वजन क्या होगा?
- 44 कि०ग्रा०
- 48 कि०ग्रा०
- 41 कि०ग्रा०
- 42 कि०ग्रा०
Q2 · medium · PYQ 2018
The average of 14, 31 and another number is 30. What is the third number?
- 40
- 45
- 35
- 36
Q3 · medium · PYQ 2024
A cricketer had a certain average of runs for his 64 innings. In his 65th inning, he is bowled out for no score on his part. This brings down his average by 2 runs. Then what is his new average of runs?
- 128
- 130
- 168
- 170
Q4 · medium · PYQ 2024
The average monthly salary of the workers in a workshop is ₹8,500. If the average monthly salary of 7 workers is ₹10,000 and average monthly salary of the rest is ₹7,800, the total number of workers in the workshop is:
- 18
- 20
- 22
- 24
Q5 · medium · PYQ 2024
The average monthly income (in ₹) of certain agricultural workers is S and that of other workers is T. If the number of agricultural workers is 11 times that of other workers, then the average monthly income (in ₹) of all the workers is:
- (1/11)S + T
- (11S + T)/12
- (S + T)/2
- (S + 11T)/12