1 Answers

Option 4 : 52 kg

Given:

Total student = 12

Replaced student weight = 40kg

Increment in average = 1kg

Concept:

Average = Total sum/ Total persons

Calculation:

Let average age of 12 students = a

Sum of age of 12 students = 12a

Old student weight = 40

New student weight = N

New average weight = a + 1

∴ (12a — 40 + N)/12 = a + 1

⇒ 12a — 40 + N = 12a + 12

⇒ 12a —40 + N = 12a + 12

⇒ N = 12 + 40

⇒ N = 52

New student weight = 52 kg

Shortcut Trick

Formula used:

Weight of new student = Previous average weight + increase in average weight × number of students.

Calculations:

Weight of the new student = 40 + 1 × 12 = 52 kg

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