Q&A - P5 Math

[MathIzzzFun]

aiong:

Dear all


I need help on this question:-
Joshua counted the number of digits of all the page numbers in an encyclopedia. He found that a total of 1359 digits were used. How many pages were there in the book?

Thank you

pg 1 to pg 9 --> 9 digits
pg 10 - 99 --> 90 x 2 = 180 digits
Total (pg 1 tp pg 99) --> 189 digits

Number of digits in 3-digit page numbers = 1359-189 = 1170
1170/3 = 390
390 pages from page 100 --> 100+390-1 = 489

Total 489 pages.

cheers.

[aiong]

Thank you so much, but the answer is 390, do you know why?

[MathIzzzFun]

aiong:

Thank you so much, but the answer is 390, do you know why?

error in answer key...390 is the number of 3-digit pages.
is this a past year exam question ?

cheers.

[aiong]

Hi


No, is current math test question, thank you

[Jamesbond]

aiong:

Dear all


I need help on this question:-
Joshua counted the number of digits of all the page numbers in an encyclopedia. He found that a total of 1359 digits were used. How many pages were there in the book?

Thank you

1 to 9--------9 digits
10 to 99-----180 digits
1359-9-180=1170
1170/3=390(No of 3 digit numbers)
390+99=489.

[ponyo]

aiong:

Dear all


I need help on this question:-
Joshua counted the number of digits of all the page numbers in an encyclopedia. He found that a total of 1359 digits were used. How many pages were there in the book?

Thank you

Pages 1-9 are single digits. No of pages =9
Pages 10-99 are double digits. No of pages = 99-10+1=90
Pages 100-999 are triple digits. No of pages =999-100+1=900

No of single digits: 9*1=9
No of double digits:90*2=180
No of triple digits:900*3=2700

Since total = 1359, the no of pages is triple digit.

Total of single digit+double digit=9+180=189

To get to 1359 digits, 1170 (=1359-189) more digits are needed.

1170/3=390 pages from page 100 ('cos we know it is a 3 digit page no)

Hence the page no =390+100-1=489

Answer: 489 pages in the encyclopedia

[aiong]

Thank you so much for your great help,


MathIzzzFun, Jamesbond and ponyo. Cheers

[chloecube]

MathIzzzFun:

chloecube:

in a stadium, the number of girls is equal to the number of men. there are 252 females altogether, 7/9 of the children and 2/3 of the adults are females.

a) find the number of girls
b) find the difference in the number of children and adults

Children --> 9 units
Girls --> 7 units
Boys --> 2 units
Men --> 7 units (1/3 of adults)
Women --> 14 units
Adults --> 21 units

Total females --> 7 units + 14 units = 21 units --> 252
1 unit --> 12

Number of girls --> 7 x 12 = 84
Difference in number of adults and children
--> 21 units - 9 units
= 12 units
= 12 x 12 = 144

cheers.

i see, so the method here is to make the number of girls and men units to the same

thks!

[chloecube]

Aisikin:

in a stadium, the number of girls is equal to the number of men. there are 252 females altogether, 7/9 of the children and 2/3 of the adults are females.

a) find the number of girls
b) find the difference in the number of children and adults

Let the total number of Children be 9 units.
=> there are 7units of girl. Since the number of girls is same as the number of men, there will also be 7 units of men.
Men made up 1/3 of the adult, thus 2/3 of the adult is women, which is 14units.

7units of girls and 14units of women = 252 females => 1 unit = 12.

a) number of girls = 7 units x 12 = 84 girls.
b) total children is 9units = 9x12 = 108
total adult is 21units = 21x12 = 252
difference is 252-108 = 144.

thks

[aiong]

Confirmed, answer is 489. you are right. cheers