MATHS!!!!!20 point!!!help!!!

1.if a=7/4b and 2b=3c,find a:b:c

a = 7/4 b ---> a : b = 7 : 4
2b = 3c --> b : c = 3 : 2

therefore a : b : c = 21 : 12 : 8


2.Sam,ANdy and Sue share a box of chocolates in the ratio 4:6:5.If Sam gets 20 chocolates,find the total number of chocolates in the box

Andy gets : 20/4 x 6 = 30
Sue gets : 20/4 x 5 = 25

total no. of chocolates : 20+30+25 = 75


3.A car travels 180 km in 2.5 hours.Find the distance (in km) that the car travels in 90 minutes if its speed is increased by 2m/s

the car original speed :
180 x 1000 / (2.5 x 60 x 60)
= 20 m/s

the distance of the car travelled with increased speed :

(20 + 2) x 90 x 60 / 1000
= 118.8 km


4.A two-digit number is given and the sum of its digits is 7.If the tens digit and the units digit are interchanged,then the new number is greater than the original number by 45.Find the original number.

Let the original number be AB

A + B = 7 ---------- (1)

(10B + A) - (10A + B) = 45
9B - 9A = 45
B - A = 5 ----------(2)

(1) + (2) : 2B = 12
B = 6

therefore A = 7 - 6 = 1

Ans : The original number is 16.