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Question

there were 48 pupils in the hall. 3/4 of them were girls. when some of the girls left the hall. the no. of girls who remained was 3/7 of the total no.of pupils. How many pupils are there in the hall now?

 

pls help. 

Did i understand wrongly that remaining = 3/7 * 48 = ?  ( the ans in decimal)???? thanks.

Answer

Method 1 :
1 – 3/4 = 1/4
(1/4) x 48 = 12
1 – 3/7 = 4/7 ——- 12
1/7 ——- 12/4 = 3
7/7 ——- 3 x 7 = 21

Method 2 :
(3/4) x 48 = 36 (girls at first)
48 – 36 = 12 (boys)
1 – 3/7 = 4/7 ——- 12
1/7 ——- 12/4 = 3
3/7 ——- 3 x 3 = 9 (girls who remained)
9 + 12 = 21

Ans : 21 pupils.

 

1 Reply 0 Likes

hi tay, once again. thanks for help. 

1 Reply 0 Likes

Hi atm, it is my pleasure.

0 Replies 0 Likes

Hi ATM, it is 3/7 of total “remaining” pupils (which has changed after some girls left). Question did not specify clearly but usually understood as this way. Try to give rephrase as “was 3/7 of the total no.of pupils remaining” or “was 3/7 of the total no.of pupils now“.

  Total Girls Boys
At first (4/4) 48 (3/4)  36 (1/4) 12
Some girls left   ?  
Balance (7/7) Ans:9+12=21#  (3/7) 9  (4/7) still 12

If 4/7 is 12 –> 1/7 is 3 –>  3/7 is 9

1 Reply 1 Like

HI SAHMOM, thank you for your explanation. 

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I think you understood wrongly.. 

Before the girl left 3/4 of 48 are girls

After the girl left, 3/7 of the new total are girls.

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