Question 129974
Let {{{a}}}= Ann's age now
Let {{{b}}}= Bill's age now
{{{a = (7/10)*b}}}
In 4 years Ann will be {{{a + 4}}}
In 4 years Bill will be {{{b + 4}}}
{{{a + 4 = (8/11)*(b + 4)}}}
substitute {{{a}}} in the 1st equation for
{{{a}}} in the last equation
{{{(7/10)*b + 4 = (8/11)*(b + 4)}}}
{{{(7/10)*b + 4 = (8/11)*b + (32/11)}}}
multiply both sides by {{{11*10}}}
{{{7*11*b + 4*11*10 = 8*10*b + 10*32}}}
{{{77b + 440 = 80b + 320}}}
{{{3b = 120}}}
{{{b = 40}}}
Bill is 40 now
check:
{{{a = (7/10)*b}}}
{{{a = (7/10)*40}}}
{{{a = 28}}}
{{{a + 4 = (8/11)*(b + 4)}}}
{{{28 + 4 = (8/11)*(40 + 4)}}}
{{{32 = (8/11)*44}}}
{{{32 = 32}}}
OK