My solution:
For such questions, try to match the supposed equal parts -- the numerators.
From matching the numerators using LCM (lowest common multiple), then find the denominators.
The LCM of 3 and 2 is 6.
Joel's savings --> 3/5 = 6/10
Mathew's savings --> 2/7 = 6/21
With the help of a simple model:
. _____ 6u ____ __ 4u__ _____ 11u_____
. / \ / \ / \
Joel |---------------|---------| .
.
Mathew |---------------|--------------------------|
Mathew |---------------|--------------------------|
. \_____ ____/ \_________ __________/
. 6u 15u
.
15u - 4u = 11u
Ben --> 2 x 11u = 22u
Ben - Joel --> 22u - 10u = 12u
12u --> $24
1u --> $24 / 12 = $2
(a) Joel : Mathew : Ben --> 10 : 21 : 22
Total --> (10+21+22) x $2 = 53 x $2 = $106
