There were 120 fewer boys than girls in a school hall. After 20% of the girls left the hall and 70% more boys entered the hall,there were 321 children in the hall.how many girls remain in the hall?

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# Question

# Answer

Adwin

20% = 20/100 = 1/5

*This means 1/5 of the girls left the hall.*

70% = 70/100 = 7/10

*This means that there were originally 10 units of boys and an additional 7 units of boys entered the hall.*

**At first:**

Boys → 10 units

Girls → 10 units + 120

After 1/5 of the girls left the hall, the number of girls remaining is:

4/5 × (10 units + 120) = 8 units + 96

After 70% more boys entered the hall, the number of boys became:

10 units + 7 units = 17 units

Since there were 321 children in the hall in the end,

8 units + 96 + 17 units = 321

25 units + 96 = 321

25 units = 321 – 96

= 225

1 unit = 225 ÷ 25

= 9

8 units = 9 × 8

= 72

72 + 96 = **168 girls remaining**

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