✔ 最佳答案
1.A 2-digit number is divisible by both 2 and 5.Half this number is less than 6 times the tens digit ofthe number by 4.Find this 2-digit number.
the number is divisible by both 2 and 5 which means it is a multiple of 10
Let the number 10x ,where x is the tens digit number
6x-10x/2=4
6x-5x=4
x=4
therefore ,the number is 40
2.There are some chickens and rabbit in a cage. 1/3(分數三分一）of the rabbits were born to have 3 legs.If the total number of legs is90,Find the number of
Let the number of all rabbits be x and the number of chicken be y
(x/3)(3)+(2x/3)(4)+(2y)=90
x+8x/3+2y=90
11x/3+2y=90
11x+6y=270
by substitution , we have x=18 ,y=12
Therefore ,
(a)chickens
the number of chicken is 12
(b)rabbit with 4 legs
the number of rabbit with 4 legs is 2(18)/3=12
3.Kelly borrowed $4800 from a bank at an interest rate of 10%p.a .for 8 months.Wendy borrow$20000 from the same bank at an interest rate of 24%p.a.If Wendy paid $80 more as interest than Kelly,how long did Wendy borrow the money?
Let n be the moths that Wendy borrows the money
Wendy paid $80 more as interest than Kelly
[20000(1+0.24/12)^n-20000]-[4800(1+0.1/12)^8-4800]=80
20000(1.02)^n=80+4800(1.07)+15200
(1.02)^n=1.020
take log on both sides
nlog(1.02)=log(1.020)
n=log(1.020)/log(1.02)~1.023
Therefore,Wendy borrow the money for 1.023 months
