Maths P.6 Quick !!!!!!!!!!!!!

1)

A+B = 56

A^2+2AB+B^2=3136

A^2-2AB+B^2+4AB=3136

(A-B)^2+4AB=3136

(A-B)^2=3136-4AB

A-B=sqrt ( 3136 -4AB)

consider A can write as a x c and B can write as a x b

then the LCM = axbxc and HCF = a

the , we have 80 = abc and 8=a

=> bc=10

A-B=sqrt ( 3136 -4AB) = sqrt ( 3136 - 4 x 8^2 x 10) = 24 //

3) A lion can run 46 km per hour. It can run 23 km in______ mins.

Ans:

distance / time = speed

23 / time = 46

time = 0.5 hour = 30 mins //

4) A wolf can run 36 km per hour. It can run 9 km in _____ mins.

Ans:

distance / time = speed

9 / time = 36

time = 1/3 hour = 20 mins//

5) John jogs at a speed of 1.5 m per second. How many minutes and second does it -take for him to jog 1380 m? ( Give me the solution)

distance / time = speed

1380 / time = 1.5

time = 920 seconds = 15 x 60 + 20 seconds

since 1 minute= 60 seconds ,

so 15 x 60 + 20 seconds = 15 minutes and 20 seconds.


2009-06-23 13:32:47 補充：
4) A wolf can run 36 km per hour. It can run 9 km in _____ mins.

Ans:

distance / time = speed

9 / time = 36

time = 1/4 hour = 15 mins//

1) Assume A > B, AB = 8*80, A + B = 56,
(A - B)^2 = (A + B)^2 - 4AB = 576
A - B = 24

1)
HCF of A & B = 8
LCM of A & B = 80
A + B = 56

First, factorize (因式分解) 8 & 80,
8 = 2³
80 = 2^4 × 5

From this, we can know 8 × 2 × 5 = 80
Since 8 is a common factor (公因數) of A and B,
A = 8m
B = 8n
mn = 2 × 5 = 10

A + B = 8m + 8n = 8(m+n) = 56
So, m+n = 7

mn = 10
m+n = 7
m= 2 , n=5

A = 8m = 8×2 = 16
B = 8n = 8×5 = 40
Their difference = 40 - 16 = 24

2)
Heptagonal pyramid

3)
The speed
= 46km/h
= 23km/0.5h
= 23km/0.5×60min
= 23km/30min

4)
The speed
= 36km/h
= 9km/0.25h
= 9km/0.25×60min
= 9km/15min

5)
1380 ÷ 1.5
= 920 sec
= 15 1/3 min
= 15 min (1/3)×60 sec
= 15 min 20 sec

1)A=16
B=40


The difference between A and B is:


B-A
=40-16
=22 //


2)Heptagon pyramid //


3)30mins //


4)15mins //


5) 1380/1.5
=920 s.
=15min. 20s. //

3) 30
4) 15
5) 1380/1.5=920 seconds = 15minutes20seconds
第一第二唔識