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