中一maths

The value of a is 4 times that of b.If their sum is 45,find the value of a.
a=4b-------(1)
a+b=45----(2)
From (1):
b=a/4------(3)
Put (3) into (2):
a+(a/4) = 45
(4a+a)/4=45
4a+a=180
5a=180
a=36
Hope I can help you
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a=4b
a+b=45
ie (4b)+b=45
5b=45
b=9

sub. b=9 into the formula a=4b
ie a=4*9
=36

Help this can help