CAT 2017 Slot 2QA Question 6

Change in AverageEasy

The average height of 22 toddlers increases by 2 inches when two of them leave this group. If the average height of these two toddlers is one-third the average height of the original 22, then the average height, in inches, of the remaining 20 toddlers is

Answer & solution

Correct answer: 32

  • A

    30

  • B

    28

  • 32

  • D

    26

Solution

Easy

Conserve total height. Let the original average be xx; express the two leavers' total and the remaining 2020 toddlers' total, then equate to 22x22x and solve.

1

Set up the totals. Original average xx, so total =22x=22x. The two who leave average x3\tfrac{x}{3}, and the remaining 2020 average x+2x+2.

22x=2x3+20(x+2)\begin{aligned} &22x=2\cdot\frac{x}{3}+20\,(x+2) \end{aligned}
2

Solve for xx. Clear the fraction and collect terms.

22x=2x3+20x+40 66x=2x+60x+120(×3) 4x=120  x=30\begin{aligned} &22x=\frac{2x}{3}+20x+40\\ &\Rightarrow\ 66x=2x+60x+120 \quad\text{(}\times3\text{)}\\ &\Rightarrow\ 4x=120\ \Rightarrow\ x=30 \end{aligned}
3

Average of the remaining 2020. It is x+2x+2.

30+2=32\begin{aligned} &30+2=32 \end{aligned}
Average of remaining 20=32 inches\text{Average of remaining }20=32\ \text{inches}

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CAT 2017 Slot 2 QA Q6: The average height of 22 toddlers increases by 2 inches when two of them leave this group. If the average heig — Solution | TheCATExam